Hey the art itself looks great but I think you are using too many colors which in turn will make it harder to have objects stand out since you will invariably have more noise.
An example of this would be if you look at your left and rightmost columns for each palette, the near white colors are mostly identical, you could simply do with 1 or maybe 2 white colors. The dark shades all have too much overlap as well, if you selectively remove some of them you will actually have color groups that nicely blend in with each other which then creates more cohesion.
If you need some examples I'd be happy to draw one up for you. (do not have access to my drawing tools right now)
Hope this helped and I look forward to seeing more of your game, it looks promising :)