Fundamentally, the reason the Wx radar is fitted is so we can avoid turbulence associated with Cbs. So, the first thing you should determine (from the met briefing pack) is the likelihood of their presence. Also, you have don't have to have rain to get a ride that will make your eyeballs hit their limit switches.
So, moving on it's not the colour per se that determines the movement of the air around the water that is displayed on the display. I'll give you that white/magenta or what ever colour is designated to the highest return, is probably due to rainfall from Cb, which are probably best avoided, but not always. What you need to avoid are the areas containing sudden and abrupt transitions in the patterns displayed. Avoiding an area purely due to colour alone may only add to track miles and give no smoother ride. Hooks, swirls, solid lines and areas with high contrast are also best given a wide berth. And here's the weird one, not all Cb's give a rough ride. But I'll be buggered if I can tell which ones are the friendly ones in advance.
PM