it's not nearly as bad as you seem to think!
I've spotted a couple things that could be fixed up, though.
AT-STs are a darker shade of gray, especially with the legs, and where they attach to the 'body' of the vehicle.
The viewports need to be painted a gloss black, and remember that there are only two windows, the bump in between them should remain the color of the body.
Also, you might want to try a wash, probably with an even darker gray, and maybe some brown near the feet.
You might want to do a google image search for "atst" to find reference pictures.
Also, white is a pain in the butt, ain't it?