There is a discussion on that in the KAL somewhere. I'll try to explain from my memory (?).
Use 5 Foreground colors and 5 Background colors
in the pattern when it calls for the B numbers you will use them twice. For instance, B1 and B2 in the pattern are both knit with your FIRST B color. B3 and B4 are both knit with your 2nd B color, and so on. Does that make sense?
It might be in the FAQ discussion, but unfortunately I can't quite remember where I saw it. Hope that helps!