Acceptable to Compress 2D pixel-perfect sprites with limited colours?

Hi. I have some rather large spritesheets of pixel-perfect art, however there's very few colours (generally 4). I've always heard that you should never compress pixel-perfect spritesheets, but is any image quality actually lost if there's only a handful of colours present?

Bonus Question: Is it acceptable to use crunch compression as well? Does it lower the image quality of an image with <5 colours?

Example spritesheet: