Cured epoxy is not UV stable, and will degrade with prolonged UV exposure. Depending on the color and opacity of the tints you're using (e.g., mica powders, pigment dispersions, or universal tints), you may be able to boost UV resistance a little, but photodegradation is the eventual outcome. The suface will gradually lose gloss, turn yellow and break down.
To ensure UV protection for your epoxy surfaces that will or may be exposed to UV light for prolonged periods, apply a clear, UV-stable varnish over the cured epoxy, as directed.