Idgaf that supposedly yautjas only see infrared without their biomasks. I don't care if that's the cannon either. In some way they can definitely see visual light in some spectrum.
Here's why:
1) Infrared, while providing heat signatures and shapes, it shows no details. You'd have to rely on touch, and devices to see most and important details
2) We see the yautjas are a detailed species. A prime example is mating season- males will show their prowess by wearing their trophies, scars on display, armor or none. A female wouldn't be able to see those details using infrared, and we see most yautja on Yautja Prime in "Predator Killer of Killers" most are without masks.
3) Many Earth species use infrared sensors, but still see in visual light. However, salmon and bullfrogs can switch their vision into infrared to see in very foggy or low visibility areas, then return to using their spectrum of visual light. However, those are the closest known species who can see in full infrared.
In short, I'm a confident believer, that realistically speaking, yautjas can 100% see visual light (whether red to violet like humans, or limited color).
So in short, no I don't think a yautja is only capable of seeing infrared without their mask. I do believe they can switch between infrared and visual light, because it makes more sense from a scientific standpoint while also explaining why we see them using infrared without their masks in the movies.
Mostly making this argument to validate how I'm writing the yautjas in my fanfics because they are describing details you can't see using only infrared.
