Color-coded 50 Ohm BNCs
What you are looking for is the "jacket color". You can filter on color at many online stores, for example: Brown Coax cable listed at Digikey.

Colored patch cables are not common, so buy a reel and add the connectors yourself. 

However, it is probably an expensive way of solving the problem, which could possibly be resolved with silicon cable markers or other methods suggested in the comments.