Its everywhere, 255,255,255,0 👻🎃 but why do we use 255? The answer is so short I'm not sure it needs a post but hey. 255 is the largest unsigned 8 bit interger (u8) for short,
Take the rgb colour channels at a max of 255 and you get 16,77.216 possible colors, so if you ever wondered why it's so hard to pick a pallette, thank the stars you are not using a 16bit colour space (that's probably not correct)
Anyway, 255, youll see it everywhere u8 is used.