A visibility study conducted by the College of Safety (by Prof. H.H. Hurt) at the University of Southern California found that high visibility upper clothing was much more frequently noted by cage drivers than dark clothes. That, certainly, was no surprise.

However, there was a surprise: Bright shirts with long bright sleeves were, by far, more noted (seen) than those with short sleeves. It seems that a rider (motorcycle rider in this study) with a bright short sleeved shirt tended to be seen more as a sign than a person. When equally bright arms were added, the cage drivers were much more likely to see a complete person and react accordingly.

Motorcycle riders with black bikes and black leather jackets were pretty much invisible.
Black bikes (either kind) and especially black clothing makes a rider dissappear.

Joe