A forest is one of the most beautiful things in creation.
so take a look at some refs
in fact, before you go any farther just googleimage search forest
Take a look at the greens and oranges and reds. Really look at the colors and let them soak in, even bring them into photoshop or flash and start building a rough pallet from them on the side of your screen. You will be astonished at the colors you end up with.
The sword next to the couch looks a little out of place, and I'm not certain I love the color of the ninja.
These again are by no means bad drawings. They could be much better though if you paid a little more attention to your pallets.