Here's a tutorial on how to hue shift. what is hue shifting? it's changing the hue of a color as your colors get brighter.
now here's a sprite without any hue shifting in it:

it looks very plain doesn't it? now how to make it look better without raising the color count? hmm.... let's use hue shifting! now to explain hue shifting a little better, lets show two palettes, one with and one without hue shifting:
now this first one is a palette without any hue shifting:

pretty bland huh?
now here's a palette with hue shifting in it. it has moved from a purple to a yellow.

now this one looks a lot better doesn't it?
now lets apply it to the sprite. I'm only changing the skin color, but you should get the basic idea.

you see? the sprite looks better. and since hue shifting is a major part of pixel art, it will help to use it.
but since that is a pretty bad example of what hue shifting looks like, here's an example of hue shifting on a better piece.

every inch of this piece has hue shifting in it. hue shifting is a way to cut down on colors, and at the same time, make something look cool. If you do it right.
this is my first tut, so help if it's not that good please.