I find this very hard to look at. The yellow just meshes everywhere and blooms into the viewer's face too much. Then there's the fact that it makes the characters less distinguishable, thus degrading from the focal point of the wallpaper. The black background does not help, as it only serves to add to the contrasting bloom and make the picture look like a giant bucket of yellow paint was spilled onto the wallpaper. I would suggest cleaning it up a bit. Work on vectoring the characters more if you haven't already, and make the color a little more simmer than the yellow you have now. Then add a background and we can take it from there.