Use Colour Responsibly Stamp

Man, I love using colours. Unnatural colours, too-- the more "this does not appear in nature", the better! Bright orange, neon yellow-green, vivid pink.
But for the love of god, don't mix them. Don't make a design made up of 10 colours made with 100% saturation and brightness. No, the addition of black to it doesn't necessarily make it better.

If it's neon yellow, pink, and cyan, with some good old bright green for flavor-- stop. I don't care how COOL and EDGY and HARDCORE you think you are, it fucking hurts to look at, and that's not a good character design. A good design should be pleasant to look at.

Use your head and learn what colour theory is.