Depends entirely on features and how it looks and the weather and where I'm going. Black is slimming and I like it but I have colours as well. I even wear a vile vomit pattern if all the other full-zip jerseys (rare in women's) are in the wash and I'm wearing bibs. If you're worried about visibility, use lights (batteries are cheaper than a taxi home from hospital) and look for reflective trim (there's some research around saying that, certainly for night, reflectivity is more important than colour). Lots of drivers will look but not see, whether you're dressed like a praying mantis or a ninja.