The colours are too bright, and the ground is a bit messy, but otherwise it's pretty good for second try. And maybe consider working on those shadows.

It's very good for a second one =) Take care about corners (maybe it will be better to make a corner line from the left pixel of two). And there is an issue with green color. It's too acid =)

Thanks!
Well I used the MsPaint palette with some additions. I'll try to experiment with the colour a bit more.

Light green. The design is ok but I'm not sure about the color.