+1 on yellow, in any weather.

It's not for the drivers who won't see you regardless of what you're wearing. It's for drivers who are paying attention, who will see you at least a quarter-mile sooner than if you weren't wearing hi-viz, and will have that much more time to respond to your presence.

Make a note of this next time you're in your car and see someone wearing hi-viz. Look for someone else at approximately the same distance. See how much easier it was to pick out the one in hi-viz.