Raw shrimp are gray in color and more translucent. You’ll know they’re done stir-frying when they’re pink or pink-and-white and opaque, rather than gray. They will also start to curl into themselves.   However, this all happens very fast, at times within a 90-second time span, so be very careful not to overcook the shrimp when you first add them to the sauteed vegetables, because they'll still simmer with the sauce for another 4-5 minutes so you don't need to worry too much about doneness.