It is easy to shorten both potlife and cure time using certain chemicals, but slowing down the reaction isn't so easy. One way to change working times is with temperature. An 18 degree F change in temperature will either half or double the potlife. It will also greatly affect the thickness of the epoxy. Increasing the temperature decreases the viscosity of the epoxy noticeably.
Epoxies also tend to yellow and chalk in sunlight.
Under UV light white epoxy will generally turn a straw color. Some epoxies are more UV resistant, and less yellowing, than others. Generally epoxies used for durability outside are topcoated with other paints or enamels that don't yellow and retain their gloss. There are water-based epoxies and epoxies that go on underwater. There are even lead enhanced epoxies used around radioactive sources.