If the spikes are meant to be a hazard, and the green guy is the player, then you might want to make the spike narrower. As is they look more like they would make an uncomfortable seat rather than a threat of impalation (that even a word?), nevermind impalement. If they are narrower you may also find them easier to shade without the dither.
Their colour is also confusing, until I read the text I thought they were the tops of trees in the background (the dither doesn't help in this regard either). Consider what material they are, standard metal death-spikes, woody thorns, whatever, then colour and shade accordingly.
In regards to palette, I'd recommend you not start with a premade palette unless for some reason you must, but pick colours as you go, using existing ones where you can and creating new ones as you must, then performing a consolidation pass at the end.