The C64 background colors are not a desktop, but they are so iconic that I couldn't leave them out. It's not easy to pinpoint the exact colors, but a guy known as pepto did a fantastic job re-engineering the full palette. These are the colors he calculated for 50% Brightness, 100% Contrast and 50% Color, which is what he set as default values. Visit the linked Colodore website if you want to dive deeper.