Here is a chart that walks you through the cable colors used on British Motorcycles from the 1960s and 1970s that have Lucas electrics fitted.
You should be aware that Wipac were also around at the same time (as were Miller, to a lesser extent) and they used some different color cables in their schematics and harnesses.
Since Lucas were the main electrical vendor of the time, and make up the majority by some considerable margin, I have focused solely on Lucas in this chart.
This is also available as a PDF download in case you want to print it out to keep handy in your workshop!
This article is from a series of Handy Workshop Guides I have put together.
These may be of interest to you: