Please just transparify the background, instead of trying to make the color match one of the site themes...as the given color clashes with other themes other users use, and the background is not a necessity to the piece itself.

Sending back...

 its ok but I think it would look better without dithering.Why dither if you use 25 colors which is relatively lot for this image?

EDIT:oops... I didnt see the Manupixs comment until now 

Manupix is correct. We haven't added because of the uselss BG. You can use something like www.iaza.com if you need to.

Nice, welcome!

You will probably be asked to remove the bg, or make it interesting (a patch of shadow on the ground might help).

Dithering is a bit on the too much and uncontrolled side.

Nice colors, but you should try to make a more integrated palette (interacting instead of separate color ramps) and recycle colors throughout the piece.