Change background for item summary page

Hi guys

I am new to Opencart and am extremely impressed with it so far, I am using the latest version to build a site for designer baby clothes.

I have successfuly changed the look of the site to meet the customers design requirements but have come across bit of a stumbling block. The clothes are to be catagorized for boys and girls. When a boy clothing item is selected he would like a blue background image on the summary page, surrounding the photo and text and for the girl items he would like this to be pink.

what would be the best way to do this?

Thanks in advance

Andy