False cat, true cat. Green cat, blue cat.
Green cat is a lie, or the forgery of a mind addled with color blindness. The cat, to anyone with working eyes, is a shade of teal or cyan.
Teal: "a medium to dark greenish-blue color."
Cyan:" a greenish-blue color."
Greenish-blue. Blue, with just a hint of green. Forget everything you knew about green cat, if what you "knew" was that the feline was green. If you knew the cat was blue all along, remember what you knew.
Also the backstory claiming the cat obtained its unnatural hue from sleeping in brightly colored paint sounds a little suspicious, but that's not the point right now.