Just to clarify Gil's comment about "everything has a different light source":
The tree on the left is shaded with a single light from directly to the right. The face, neck and body of the guy in red are shaded with a light from the right. His left leg is pillow shaded, while his right leg is shaded with light from the right again. His shadow is crisp and dark, but cast directly downward, from a light source up above (his hair is shaded the same way). The guy in green has a similar affliction - however his shirt is shaded from the topright, rather than just the right. His hair has inverse pillow shading, while his legs suffer the same fate as the guy in red. He has a vertically cast shadow as well. The right-most tree, however, is shaded on the trunk from the left, but on the branches and leaves from above. I think the only light source that you haven't used is one from directly below.
Also, people continue to comment on the background colors because there is absolutely no indication that you intend to not use these pure MS Paint shades in the final product. The green in the grass can be found in the tree's leaves, and many of the tones used on your characters are massively over-saturated (except for their skin, which is ashen and dull). Folks will only assume that you will make massive improvements if there is some hint of that in the existing artwork. So please do not get snappy when people give you valid crits when there is every reason to expect that these crits will still apply even after detail is added. A majority of the responses have encouraged you to re-examine the fundamentals of this image, and you have done nothing of the sort - you've made minor superficial changes that do not address any of the real problems with this piece. You're wasting everyone's (including your own) time by continuing to post these miniscule updates that ignore everyone's feedback.
Continuing with this piece without addressing the massive fundamental errors in its construction is a waste of time; you are not learning anything, you are only continuing to practice bad art and bad design and bad color theory. A rough gem is worth a lot more than polished garbage.