is this possible? i want to put my adsense ads over a background image and it looks bad if the ads have to have a background color
No it's not possible without adjusting the adsense code and that would be a violation of tems and conditions. If you wish to blend simply make the BG color the same as the BG color of your template. if there is an image on the background where you want to put the adsense code, then consider changing either the position of the adsense code or the background image itself so that there remains only one colour where the code will go.