A black can absorbs radiation more efficiently than does a shiny can, which reflects most of the radiation away, so the black can heats up fastest. It also cools down fastest. Both absorption and emission are determined by the same parameter, the emissivity.

The temperature as a function of time is given by Newton's Law of Cooling (this is actually just a good approximation of what happens).

T(t) = T_env + (T_init - T_env)*e^-λt

where T_env is the temperature of the surrounding environment,
T_init is the initial temperature of the object,
and λ is a measure of how quickly the temperature change occurs.