It makes me so mad and sad when I see so called "Artists" telling other people how NOT to design a character. For not using face markings or bright colors or colors which won´t "match with eachother".
You stupid people.. everyone has a different taste.
I like different characters. I mean.. have a look.
Katinka´s or J.B.`s color palette and markings are so simple some people might call them boring but they still are great:
Then there are those people against rainbow manes / tails. Wtf is wrong with you? If someone likes rainbows, let them design rainbow characters.
You can put tons of markings to your character´s fur pattern if that makes you happy. Nobody should care but you. I prefer them simple but hey, sometimes tons of markings are an eye catcher.
Weird markings are cool too.
Go as colorful as you want. Even if people say, those colors don´t match. Your character. Your choice of colors.
Use Horns, Hair, Fishtails, Elements, what ever. Nobody can forbid that.
Create tons of characters if you want to. Make them all look different or the same. What counts is, that you´re happy with them.