Further contrast could be made by having different threads on the helices of the colours, eg one cable being like slices, one like splines, and one like a screw thread.
You could check out colour blindness, to know which mixtures are likely to be difficult for some people to differentiate. There are for example two different sorts of red detector in the eyes, carried on the X chromosones, so men (X-Y) see reds in one of two different distinct shades [Men colour matching mixtures with pure colours fall into two categories], whereas some women (X-X) have superior colour sensing since they can have both types of red color detectors in their eyes.
Bear in mind many street lights are yellow so some combinations like yellow and white might look much like plain yellow under street lights.