Black Flag used to be accompanied with a number - I think 1 to 5. I recall runway blocked, ice and crosswind. This allowed simplification when the colour states were passed from Ops via a phone (no nifty electronics in the 60s)to be recorded on a board by the duty auth i.e. Waddington is White and Binbrook is Black 3 (which I think was crosswind) etc for all UK bases.