To make up for Drew's lack of flourish and suspense when reading the price, they took the opportunity to program him out of the game.
I think that's part of it, but if you look at other game shows on the air right now (I'm thinking Jeopardy and Wheel mostly), they have sets that light up and change color too. Wheel has video walls everywhere, and the last time I paid attention, the one behind the players had a video loop. Not enough to be really distracting but you knew it was there. Their sets feel appropriate for their atmospheres--Jeopardy is really serious and Wheel is more relaxed and fun.
Price has always been kind of like an all-out party atmosphere, and I think their set and color choices reflect that. There's always something flashing, changing color, animating, something; enough to get a casual channel-changer to tune in and stay tuned. Used to be seeing Bob Barker was enough to do that, but without him I agree with Flerbert, they have to up their game in other ways to grab and hold attention.
On the topic of more light vs less light--I actually think the set is lit a lot less brightly than it used to be overall, since so many pieces of it light up on their own and they don't need to flood the stage quite so much. I keep an eye on the doors to see that; if you watch the parts of them that don't light up, for the most part they're not lit brightly at all. The only exceptions are when someone is standing next to them. Door #1 really shows it, since anytime they turn the lights up even a little, that orange color really picks it up.