as with ur cowboy ur colours are really washed out.
made a few quick changes here...

blue could probably be used more sparingly than my edit but u have too many colours so i couldn't be bothered editing so many.
regardless it still is more interesting than so much grey.
it looks like what youve done here is just picked a colour every time u draw something with very little conservation.
in future try recycling colours to bring harmony to ur scene and only add new colours when u need to.