[[ Yes, it is indeed the case that according to official material published by Wizards of the Coast, drow typically have obsidian black skin. There are canonical exceptions to the rule, the most notable one being albino drow, which are known as the szarkai, who possess very light skin that can be as pale as alabaster-white. However, I realize you’re not talking about these rare exceptions, and you’re right about “dark”, “very dark” and “black” as normal drow skin colors. There are degrees of variation among average drow skin tones, but the lightest color is dark gray. I’ve personally never seen mentioned in any source material, be they handbooks, supplements, games, novels, etc, the existence of drow with naturally purple, blue, or otherwise colored skin.
That being said, the phenomenon you’re observing in artwork I believe is due more to the specifics of making art. Very strong emphasis on “I believe” here, because there really could be a million different reasons why people depict drow the way that they do. I imagine that while most people probably first encountered drow in D&D-related material, they’ve since taken the concept of drow into homebrew games and original settings in which really, anything goes. Heck, even when staying within official/canonical D&D settings, people might make drow characters something other than black-skinned because, like you said, people can interpret it however. The canonical skin tones could also just be one of those things that’s ignored about drow canon much like how many ignore and/or forget that canonically, on average, female drow are larger than male drow males. Here’s one of many references to this fact:
(Source: Out of the Abyss)
The text in the above image might be too small to read, but it says:
Drow males are smaller than the females. Their armor is snug, flexible and quiet. Web shawls and cloaks made from giant spider hide are popular adornments.
I believe though that most artists who illustrate drow with the intention of making them look true to canon, that is, with obsidian black skin, don’t end up doing so because of, fundamentally, nothing is truly absolutely black. Descriptions like, “ebony black skin”, “obsidian black skin”, and “skin as dark as a moonless night” are romanticizations, written with the intention to convey something to our imaginations. It isn’t always possible to translate that kind of thing, especially with romanticization, into art, nor should it always be done. However, even if one set out to try to depict a character with pure black skin, well, they’d very much have their work cut out for them.
I’m not the most qualified to talk about this since my personal artistic journey is not where it should be, but I know enough of the basics to hopefully be able to shed some light on why people don’t (and shouldn’t) just color drow straight up black. First, trying to depict anything that has to look dark, the artist is immediately restricted to a smaller portion of the normally available spectrum of values. In this context, “value” is the lightness or darkness of what it is that we see. Imagine an average day spent going about your life except that you only see in black and white. It’s not as exciting without the hues, but still, you can tell things apart by the difference in shades. This is because you have available to you the entire value spectrum from very light to very dark:
However, come nightfall, things become harder to distinguish from one another in the hypothetical black and white world. This is because the absence of light has made it so that your nice broad value spectrum got truncated so that you’re left with something like this:
This truncation of the spectrum is a bit of an exaggeration but hopefully what I’m trying to convey makes sense. When there’s a much smaller range of values to work with, it leaves very room for variance in the subject matter that you’re portraying. So, for something that’s a very dark color, its midtone would already be really dark, and unless there are harsh light conditions, the highlights would also be pretty dark. As you can imagine, a very dark object with even darker shadows and dark highlights will look, at a glance, like a dark blob. This is because something without a great deal of variance in values tends to be boring to look at, in addition to not giving the artist a lot of options in creating it.
So, to make up for the lack of variance from the restricted value spectrum for drow skin, artists turn to playing with the other two properties of color: hue and saturation. “Hue” is basically what laymen call “color”, while saturation is what’s normally thought of as how “bright” a color is. In other words, hue is responsible for the names that we give to colors, while saturation is how intense the hue is. With the black “color”, there is no hue or saturation, because black isn’t actually a color, but rather the absence of color. One of the first things that artists learn about color is that, unless there is literally no light, nothing is absolutely black. Science has actually changed this basic truth by introducing super-substances like vanta black, however, that has very little bearing when discussing fantasy art. For now, just know that even the darkest shadows shouldn’t be rendered by black pigment alone, because where there is a shadow, there has to be a light source, no matter how dim. Light of the visible spectrum always has color, but sometimes the conditions of the environment make those colors extremely desaturated. Still, the darkest shadows should be created with a combination of other colors to make something that suggests black rather than something that is actually black. This is because true blackness only exists in situations that are totally lightless, i.e. completely sealed dark rooms and black holes (and perhaps the heart of a drow Matron Mother ;P).
To render a character that’s supposed to have obsidian black skin, the artist’s choices of hue and saturation are also limited, although not nearly as much as with values. You can imply black by using any color that’s dark enough, furthermore, there are now two more variables to work with. These variables allow the artist to take advantage of the fact that our brains sometimes play tricks on us. For example, how we perceive color depends on relative color. In other words, you could actually be surrounded by purple drow right now, you just might not know it. ;D In reality, even the blackest-looking drow done by official artists are actually all some mix of (most commonly) desaturated purples and blues. Amateur artists are doing the same thing, but you’re likely seeing a plethora of drow out there that read as purple rather than black because, simply put, those artists haven’t mastered color theory yet. How we perceive color changes constantly because color relativity is constantly changing. It takes a lot of practice and experience to get a good understanding of it, and even then, an artist can study color theory their entire lives and not understand every mystery and intricacy of it. The effective use of colors basically allows an artist to play tricks on us with optical illusions. Remember color optical illusions like this one?
Just as the little squares in each of those bigger squares are the same color, some drow in art read more as black-skinned than others because of the other colors in the image.
Let’s now look at this painting of the priestess Ilvara Mizzyrm done by an official WotC artist. She looks pretty ebony-skinned in this picture, right?
(Source: Out of the Abyss)
However, Ilvara’s skin is actually colored using desaturated reds and purples:
Here’s Ilvara again, this time with her crew:
(Source: Out of the Abyss)
Again, although they look lighter than in the previous image, we get the sense that these characters have very dark skin. However, if we focus only on the headshots:
They suddenly look much lighter, and much more blue. This is because they are, in fact, all blue:
In the above images, color of the background factors significantly in the conveyance of the characters’ skin tones. The artists of these paintings have effectively used color relativity to trick our brains. Furthermore, because we understand the Underdark to be a very dark place, our brain makes the association that these characters, even though they’re all in what are pretty well-lit area, have very dark skin.
So let’s remove the background and see what happens. Here’s an image with a plain white background that nonetheless conveys the sense that she has black skin:
(Source: Wizards of the Coast website, artist Allen Williams)
However, her skin is, again, not black, but rather a mix of other colors, including purple. That’s again the artist playing a trick on our brains with the use of relative colors, this time by utilizing the character’s clothing.
From the three examples above, we’ve seen that, in general, to make drow look less purple and more black, an effective tactic is to use desaturated colors. However, graying colors completely can make an image look boring, because it’s imposing limitations on the palette. It’s not impossible to convey very dark to black skin tone using saturated colors, as long as effective relative colors are chosen. I’m sure there are better examples out there that employ the usage of saturated colors in painting very dark skin, but I couldn’t find any that involve drow, so I’m using my own work as an example. You can see the saturated blues and purples but on the whole, the skin reads as blackish (I hope).
I’ll conclude by discussing why it isn’t a good idea to color drow with just black, other than the color theory stuff discussed before. Skin is translucent, and as such, will allow light to pass through to interact with the many layers underneath. The focus of this next image is to show how complex the interaction of light, skin and tissue truly is:
(Source: GAJINOV Z, MATIĆ M, PRĆIĆ S, ĐURAN V. Optical properties of the human skin. Serbian Journal of Dermatology and Venereology 2010; 2 (4): 135.)
Look at all of those arrows! Each one indicates the direction that light will continue to travel, and all the upward pointing ones are going to be bringing information back to your eyes. Here’s another image that, for our purposes, demonstrate something similar, namely that there’s a lot going on when light passes through the surface of skin, and we see the effects of all of it.
(Source: ANDERSON RR, PARRISH BS, PARRISH JA. The Optics of Human Skin. The Journal of Investigative Dermatology 1981; 77:14.)
There are no indications that drow skin (and flesh) behaves any differently from ours as far as how it physically reacts to light’s passage. Skin is a thin, translucent material that, when stretched over flesh and bone, allows light to penetrate. Because the flesh under a drow’s skin is not also black, while we don’t necessarily see the color of the meat below, we also no longer just see the color of the skin itself anymore. So, even if drow skin by itself is absolutely black, unless it totally absorbs all light without allowing any other pathways, drow shouldn’t look absolutely black. If drow skin did absorb all light that hit it, drow would look like the bust on the right, which is the exact same as the bust on the left but had been sprayed with a completely light-absorptive material known as vanta black (as mentioned earlier):
(Source: https://news.artnet.com/art-world/new-photos-vantablack-906158)
Because drow skin isn’t totally light-absorptive like a black hole or vanta black, it should be as varied as any skin. It would also be difficult for drow to look attractive, or really like much of anything, if they did have absolutely black, light-impermeable skin. If drow were like that, we wouldn’t be able to see any of their features, like in the above right bust. An attempt to adhere to the text is commendable, but fundamentally falls short without an understanding of the properties of skin and color theory. Even if something has the blackest skin possible, unless its skin is very different from what we know as skin, it shouldn’t be just one hue. It doesn’t matter how well-executed a piece is, it risks looking unnatural if our minds don’t detect the stuff we associate with a living creature, namely, the stuff beneath the surface. Take, for example, this lady:
You see how her skin looks sort of lifeless and monotonous? This is due to her being rendered in just grays (completely desaturated colors). The way that I look at this image, the living tissue beneath her skin isn’t lending their refractive properties to what’s above, so it makes her look more like an undead creature with dead and gray flesh underneath rather than a member of the same race as in the images above.
Finally, as great as it sounds to color drow pure black, here’s an example of what happens when it’s done:
Without mentioning the fact that skin and flesh wouldn’t refract light like the image suggests, the basic tenet of color theory is violated with the completely black areas. I’m not sure how what’s depicted above would be achieved unless a creature was made up of patches of alternating vanta black-like substance and reflective material. In other words, practically speaking, purple drow in art are a good thing and much more accurate to fantastical reality than strict adherence to the words.
I’m not savvy on the minutiae of how drow differ across the D&D multiverse, but to my knowledge, the reason that this fantasy race has so much wide appeal is due in no small part to the striking juxtaposition of their stark white hair against their very dark (ebony black) skin. I feel like deviating from this aesthetic isn’t what most are keen to do, because doing so takes away from the whole point of falling in love with it in the first place. In the color sampling gifs I posted above, one consistent thing that you can note is that the darkest areas of each character’s skin aren’t pure black. The value range is pretty limited for the painting of Ilvara in the darker setting, but for the priestess with the white background, the highlights are actually pretty far up towards white. What could be happening in the case of light purple and light blue drow is that the artists are using the same colors for their characters as they always do, but it just stands out more when there’s no background. It can also be argued that different drow, like different humans, have different refractive properties to their skin, so they look different while bathed in light. In the end, it just all comes down to relative colors.
Well, that was probably more information than you wanted or needed. XD
TL;DR version: I think that most people agree that drow have very dark skin, and most of them are actually trying to depict it with the same approach in mind. In reality, purple drow are everywhere, and are a much better and realistic phenomenon than drow colored with only grays or pure black. What you’re observing is most likely due to artists at varying stages of their artistic journeys rather than the lack of adherence to canonical drow appearance. ]]