Nice work! I'd recommend you take a look at the colors artists like Stava and Hiuru use in their artwork, try to see how they use saturation and different colors in their mixes. Picking colors is hard at first, and it can give pixel art a better look.
Edit: A bunch of Stava's EO work:
Consider basing a piece off of some of his colors just to get a feel for it.
The cake is a lie.