I don't know. I think you can have a favorite without actually owning one... without having to question whether it really is your favorite or not. Most people look at personality and ability first, then color- so it would make sense to not often have the exact color of horse that you want.
Personally, I have chestnuts. Or...atleast I thought I did. But what are my two horse's colors? Chestnut and Chestnut Tobiano xD Now I'm rather fond of it, and am actually hoping to get a chromey chestnut out of my mare when she foals.
One color I do highly dislike on any horse though is bay, unless they're very dark or very chromey. I love my trainee Noah to death but I hate his coloring.
A color that I absolutely love though? Pretty much anything dark with a bald face or a non fading black <3
the day I got him (sorry he's so gross, he came from a bad situation)
I have to say though that I LOVE our shetland pony Myss Pony's coloring though <3