Not sure what you mean by before? I've compared the one from v1.0 with v0.25 and they're identical, unless there was an older sprite pre-0.25 which I don't know about?
I mean sure for photorealistic art it wouldn't necessarily be that bright, but for stylised art, even in non-pixel artstyles it's common for the inside of the mouth to be brighter than reality. Typically it just shows that you're seeing the tongue in its normal position, obscuring the deeper parts of the mouth like the throat. Take Erahunter for example:
View attachment 4460839
Her tongue isn't up against the roof of her mouth or anything, it's just that most of what you see is tongue because the tongue sits inside the mouth.
Now you
could draw it one shade darker, like I've done here:
View attachment 4460845
And maybe that's more what you're after? But I honestly like both this one and Walnusstinte's brighter version. I don't think it's a mistake, I think it's just an artistic choice of brightness / value contrast because it's pixel art.
Yes it's not a single tooth, but it's not the tongue. It's the highlight on the upper row of teeth.
Typically for most artstyles you don't draw teeth individually, but as a row, and add highlight where the light is going to reflect the most (in this case near Crystal's two front top teeth).