A high gloss acrylic sealer is sprayed on all curb that has color. Stamped or not. This is the only thing that brings the color out and makes it pop. Liken it to a clear you put on wood to see the grains. Water based sealers DO NOT work as well, make sure it is not used on your curb. All sealers regardless of what they are will need to be reapplied. Sealer that is exposed to sunlight and UV rays will break down over time, this doesn't mean they will peel off or disappear. They will lose their luster and need to be re-emulsified. Another coat will darken all your colors like the first time and make it look nice again. This is part of Maintaining Decorative concrete.