I'm sure you mean the circuits guide. If so, what Paul said is correct. A block is normally coloured on most circuits as it will feature the stand out line or a few high quality lines in that sector. E.g. The Dru bloc at Isatis is in green as it boasts a 3* f4+, 5+, 6b, and a 7a+. It also has the best cresta run downclimb in the forest..