GG is correct... we were working on projects in Virginia almost 2 years ago, minimum background vinyl is required to meet or exceed ASTM D4956-01, 3M's 3430 exceeds that standard.
The colors are required to be reflective as well, I would look at 3M's 1170 transparent vinyl. Red-1172 and Blue-1175. If colors have to match, 3M can custom color match their transparent inks for screen-print. It's my understanding that only one printer can print full color transparent graphics on retro-reflective. - but I lost the link!