Great advice in this thread. To throw in my $.02, I've found in general that lighter colors are noticeably cooler and show dirt less, but if you want something other than the standard white, silver-beige (kind of a goldish-silverish color) shows dirt the least. I've had four vehicles (trucks/suvs/vans) in that color group (but have also owned white, black, blue, grey, green, brown, red, and silver vehicles) and the experience was the same for each in that color.
I had one SUV in that color that I didn't wash for two years (don't judge me!
), and you really couldn't tell that it hadn't been washed recently.