Hi!
The most classic look would be white and green. Depending on the look you want, verbena, petunia, nastursium, nicotana, candytuft, or any combination of them.
Or you could do some thing with yellow. I think red might get lost.
I was thinking of going yellow. I know I want some of that lime green color — whether it be some form of petunia, or sweet potato vine. Green and white is a thought too. I think red is hard. Getting something red that is a reliable bloomer all summer and lush is hard. Geraniums are the first thing that comes to mind, but they are so common.
I’ve always gone to hot pink and shades of purple. I suppose I could still do that and just ignore the door. It would still look good. 6 inches of white stuff on the ground this AM, so I have a little while to decide. LOL.