Good luck being competitive in that market. I don't know how things are around your area, but around here, we have companies that sell traffic
signs at retail for less than what we can even pay at wholesale in a lot of cases. Not to mention, some of our wholesalers like to sell wholesale to any government agency or municipality, so they can pretty much cut us
sign shop folk right out of the picture. I do think that overlay is a good way to go, but stocking those colors, as well as reflective materials and aluminum sheet is very costly. Engineer grade reflective might work for things like
signs in public parks and parking
signs and things like that, but I'm pretty sure high intensity reflective is becoming the standard these days for anything on city streets and highways.