A bright idea

While in Barcelona, I stayed at Le Meridien on La Rambla. In the lobby next to the elevators was a vase of lilies that were very peculiar; their color changed, pink to white to blue to yellow. Now how did they do that?
Up in the ceiling was a very regular looking little box hidden in the stair opening that threw a slowly changing point of colored light onto the arrangement; So slow that it was barely perceivable. I began to wonder, weren't those flowers pink this morning or am I going crazy? Just another bright idea, sometimes technology IS useful!