Colour of Panels

hi I have set up two categories sales and rental as two seperate menu items and got the categories sorted and all is ok but when i create any new products in the relevant category it show up blue and i can change it using config or display options. I you look at www.nwestrailerrental.co.uk and go into trailer sales ans select flatbed trailers you will see what i mean.

Or is there a css file a can change to make the alteration ?