An article I just read today: One Hundred And One Is Easy To Spot | The Chronicle of the Horse
Quote from the article: "Only when prompted does Scott say that he’s seen his horse the victim of predjudice thanks to his loud coloring, but he doesn’t doubt that fact.
“Definitely. Absolutely. 1000 percent,” he said. “If an Appaloosa makes a little mistake it’s like a bay horse’s big mistake.
I think it stems from them not being conventionally attractive. It's easy for people to dismiss them "Ugh, they are ugly", and not think of them beyond that. Their eyes can make them look crazy. They can be a challenge, at least mine was. I found a trainer that really helped me understand her, and ever since then we've been on the same wave length. She's the kind of horse that just gives everything her all. I've never owned a horse that's so willing to try anything I ask. I love riding a horse that's as eager to do things as I am.
People don't have to like them. People just have their preferences. In my area (mainly english) appaloosas are seen as stock horses. So it's surprising to see them in a dressage arena or at a hunter barn. I don't know how many times I've heard "I don't usually like appaloosas except yours is nice". I've had lessons where the entire lesson consisted of the instructor telling me why my appaloosa couldn't do xyz. But I've also taken her places where everyone was impressed with her (and she was the only appaloosa on the property). My main trainer loves my little appaloosa, and tells me she wishes she was younger because she could have gone far in dressage. She also has a fantastic jump and is super brave. I could pull her out of the field right now and go trail riding by myself and she'd be thrilled with the adventure.
But she's also very opinionated. At an old barn I had an issue where she keep jumping the 3 board fence because she didn't like the field she was turned out in. It's been pouring the last few days and she's grouchy at being in her stall so she tried to murder my pony through the stall window (not sure what she was thinking on that one
). She grinds her teeth on her stall door if she thinks I'm too slow with getting her dinner or turning her out. She kicks the barn if she wants to come into her stall. My husband thinks she's a little witch, but she is smart enough to go right to my husband and love on him as he is the barer of treats.
Perhaps a bit of a rambling answer, but comes down to people just have preferences/prejudices. No need to argue, just make your appaloosa the best it can be and maybe you'll change a few minds.