Had to get on my laptop for this cause mobile kept murking it oml-
I don't think official art should be used as a source of proof that a cat is an appearance or not. Such as for example- Mapleshade, this is her official art (or the ones seen that isn't the manga)
Of course she doesn't have nearly as much as Leafstar, she is pretty consecutively shown as just a plain red cat. Despite it being well-known that she's a tortoiseshell and white cat.
Or even Crookedstar! Whose jaw is mentioned as being so broken that his teeth and tongue poke out, but his official art?
Not much of either shown for the lad (and Brightheart is shown with scarring, and depictions of him on other language covers do sometimes have his jaw looking as described so ehhh)
Sol is mentioned to have mane... and tufted tail of all things, but mainly focus on the mane cause-
He's primarily shown as rather sleek despite that (and the last one he's also not even a tortoiseshell like c'mon what're you doing). Even his manga art neglects to add his mane.
Not gonna post him cause I don't want complete photo bomb- Nightheart is described as a regular black tom, but most of his official art depicts him as a tabby.
As for Leafstar's description I think it's just up to interpretation at the end of the day. To some people it does read as a tortoiseshell, and there is evidence of this- with her neck being described as cream-and-brown and her cream patches being mentioned in Ravenpaw's farewell (i'll post those sections in a minute) but with how widespread her art is both official, covers, and even mangas of her being a brown tabby (tho manga always has her with white), she's kind of fallen in a Longtail and Gorsepaw situation. Where one artistic decision has kind of taken a stranglehold of what is expected with the depiction.
But here is the sections describing her cream patches and her neck being cream and brown
Personally, I'm in the boat of torbie Leafstar- cause if they'd intended her to be a regular brown tabby with a cream underbelly (or whatever it would be best described as)- they would've described it as that in the books? The only mention of her having cream is that it's typically mentioned along with her brown coloration instead of it just being "brown with cream" it's always "cream-and-brown" or "brown-and-cream" or it's patched in rare occasions, or that her fur is mottled.
whatever the hell that means according to Warriors? Cause every other cat seems to be mottled and everyone is left scratching their head about what they mean by that (mottled stripes? mottles colors like a tortie? Spotting? The description is marked with spots or smears, but what do you mean Erin Hunters?? What do you mean by it?!)
But also with the website family tree she is kind of... torbie-esque? (not sure how accurate it is, but sure)
Just gonna throw her son in there too, which according to the site they seem (or claim to) try and stay as accurate as possible to the descriptions of the cats, but there's no telling tbh since I haven't exactly sat and studied the tree religiously. And then her specific page has her as this-
Which is... kind of odd. She can go either way, but if she's a tabby then her stripes are just going completely around. Not sure how to describe it tbh. But I wouldn't trust the profiles too much either since Brambleclaw and Leafpool are depicted as just a pale brown cats (not tabbies) and Tawnypelt appearing as a grey-brown tabby with small cream patches. The specific pages are weird that some cats are shown as tabbies and sometimes not and some are accurate and some are not so take these pages with a grain of salt tbh.
But yeah just my two cents here :,D I think you're right that interpretation can lead to people going "Yeah she's a regular brown tabby" especially since we do have a lot of regular brown cats that are just brown-and-cream (the Siamese cats and Molewhisker specifically). But interpretation can also go "yeah she's a torbie" since the cream coloration being described as patches at least once, and her description never being "brown with cream," but "brown-and-cream" or "cream-and-brown." Personally I'm on the torbie side cause it's more fun for me (and also we are neglected of torbies in canon).
but also yeah to featherdawn's point tbh... Warriors does have a bad case sometimes of not calling a cat a tortoiseshell when they are. Flickerkit being one, Newtspeck, Silverflame, Rosetail, and probably countless others. Which a lot of them have been around long enough they could just be called tortoiseshells at this point, but they're not described as such so to the "red-and-black" and "grey-and-ginger tabby" pits they go.
Tbh I hope it's a Scourge's collar and Dovewing's eyes dilemma wherein the fandom fights about it for much longer then necessary. It could make the place feel like old school Warriors Fandom again think of the possibilities.
Genuinely sorry for the huuuge post 8n8 it got away from me so fast. Leafstar is a fun character for me for legit no reason tbh.