Yellow day, white night.
However... I heard that it is actually the contrast between body and head that makes the most difference. Bright body, bright but different color head make it easiest for the brain to recognise a human form, and thus most likely to intuitively recognize a rider. I wear a red jacket and a white helmet. The multi color helmets are not visible at distance. They look solid. So black with yellow stripes simply looks black.
2007 Versys Black, V35 Bags, H&B Bars, Skidmarx Hugger.Fender Ex., Avon Distanzia, Braided Lines, Hella 65W bulbs Arrow Can, DNA Air filter, GIVI tall screen (for winter), PCIII, Baldwin Saddle. **SOLD**
2011 KTM SM-T. Crash bars, E55 Top Box, Fender extender front and rear.