Edited to add: I watched them tonight and the colors constantly change, whether the elevators are moving or not. When an elevator opens, the light over that elevator does turn blue — but it also turns blue randomly when the elevator isn’t even moving. When the elevator closes and goes down again, it does seem to turn purple. But since the colors randomly change, and the blue color change does not come until the doors open, it doesn’t seem very functional. It’s awfully pretty, though!
Apparently the new lights on the Beacon Hill station that we featured in a photo post the other day are not just for looks. We’re told they have a function, too. The lights are blue when the elevator reaches the street level, then change to purple as the elevator goes down to the platform. If this is true, it makes it easier to see which elevator to stand in front of while waiting for the door to open — as long as it’s dark enough to see them, and if you are not color-blind.