In the past, gypsum underlayments left building owners with few design options. They can be covered with carpet, tile, or other flooring as long as it’s not too heavy, but because of its compressive strength, gypsum concrete is not always an appropriate underlayment for heavier floors such as engineered or solid hardwood. Another option was to polish it to get a better sheen, but staining was not a possibility with gypsum concrete because it has no lime in it to maintain a bond with the pigment. If you wanted a polished gypsum concrete floor, your only color option was the drab gray of the subfloor.
Fortunately, advancements in metallic epoxy flooring have made it possible to cover a gypsum-based underlayment to get the elegant look of stained, polished concrete.