A really nice series of icons you've done there recently!

The rocks here are really superb. The screw though looks rather flat in comparison. I would try something like this:

I used various colors to the feather and i like more with a brown touch. The idea was create grey tones using all the colors of the palete like green, brown, blue and give still the sense of a grey tone with some colorfull. Like the rock in one of your game mockups that i like much!

For me the only decent are the 2 rocks and the feather mmm i think i can improve it a bit. The screw is very basic and the spike balls are actually horribles i will give a new try and posible at 32x32 but now i go to test other things.

That's pretty decent. Nice to see someone trying the more advanced uses of the palette. Also note that you can mix blue with the bright-green if you want something closer to grey, not as good as the more effective cyan + pink f.ex, but still better than the pretty strong green or blue on their own. 

Not sure about the brown in the feather though, why not use the medium grey there?...