Professional printing has always used a four-color, or CMYK, format. CMYK breaks down like this: C=cyan, M=magenta, Y=yellow, K=key color for contrast (typically black values). Having said this, there are some online printshops using the three-color, or screen/web/RGB format. RGB breaks down as: R=red, G=green, B=blue. Check with the printshop to find out what color values they prefer you to set up.