My only theory would be between Lisa's red dress, the red car, and a red shirt on Bart, they went with a blue shirt to give some contrast. I imagine a conversation going a bit like this "There's a lot of red in that artwork." "Well I can change the car color or I can change clothes colors" "Nah, red is a good sports car color. Didn't Bart wear a blue shirt for a while?" "OK, blue shirt it is"