Kamikuza said..
To answer the OP: to make it easy to spot which way around the bar is, when you're scrabbling for it.
Red, yellow, pink, doesn't matter what color it is because you're not a boat and you're not advertising your position and heading to other vessels.
Best color coded bar I've used is the Flysurfer Infinity 1. Red on the left, black on the right - fine; but the rather than little letters saying "wrong way" on the back, there's a bar-wide white stripe. High contrast, easy to spot and react to.
I know what the colours are for, just dont like the choice of colours.
For example after a wipeout I normally use my right hand to grab the bar which is part way underwater. The black on the right is hard to see under water. Most brands use black on the right with the exception of Naish who use yellow on the right. Makes more sense, instead of having to look for your bar, boom just grab the yellow.
The white stripe sounds like a good idea.