I'm sure he had several pictures of the car and it had the same color in those pictures.
His wife's appreciation of colors or lack thereof is his problem not yours.

Deposit was made, the car was as described, keep the deposit.

The only incentive for a seller to even accept a deposit in the first place is the calculated gamble that the buyer will lose it. A refundable deposit makes zero financial sense for the seller, and creates a totally asymmetric win/lose contract.

The solution is to never accept a deposit.
"You want the car? Come back with the money. First come, first served."

My wife is dying to know if you returned the deposit