As somebody whose feral characters are pretty much all unnatural colors and markings, I have a line between what constitutes as just a fantasy critter and a full-blown sparkledog.
I don't mind oddly-colored characters, nor do I mind ones with elaborate patterns on their fur, or even the odd accessory or two as long as it doesn't look like it came from Hot Topic and has a logical explanation to go along with it. It can be very pretty and interesting when colors that don't occur on existing mammals get put onto fictional mammal characters, along with differentiating features such as uniquely shaped tails and ears or extra tufts of fur. Realism bores me, and I like to see all the neat and exciting things people do to break it.
What I do mind is when somebody's characters look like the 70s somehow condensed itself into a fuzzy animal, or like a blacklight poster climbed off of a stoner's wall and walked away, or make me feel like I drank an entire lava lamp before looking at them. I also don't understand how or why it became a thing to put human clothing and hairstyles on a four-legged clearly not-human character. Basically, if my eyes take on minds of their own and desperately try to escape their own sockets, I'm looking at what I consider a sparklebeast.
I'd lump tired and overdone color schemes like red on black in with it as well, but I'm a lot more tolerable of that than I am of critters made entirely out of sidewalk chalk.
