Cardigans have two base colors, red and black. All the other "colors" seen are from color patterns and modifiers on them. Like in Pembrokes, red is dominant to black and there are no bi-blacks in either breed. Sable, what Peggy said, except there has been some speculation that it may be both a color and a color pattern. For a good reference on Cardigan colors go to:
http://www.phi-vestavia.com/cardigan_colors.htm
Cardigans have a bunch of modifiers. so there can be a real rainbow of colors that can appear in them. Pembrokes, there are bluies (not the same as merle) and agouti that I know of.
Debbie