Originally Posted by ken cummings
The black works just fine. As I understand it the retroreflective beads are in a thin clear layer on the surface of the tape with a black layer underneath. When the tape, your eyes, and the light source line up you see a bright white area. Off the best angle it goes grey then black. The black absorbs any off-angle light so it appears black.
Off-angle light is also reflected back roughly in the same direction from which it came. Thus, the orientation of the reflector to the viewer doesn't matter. This is what makes this material so much more versitile than molded reflectors, which only work well at a discrete, usually small, number of angles.
Sorry if that's too much information; I use this stuff in my research and can't help myself from sharing.