It happens sometimes, where they won't take any prey items but a certain color. It is rare. I had one that did it for about three months, then stopped being picky.
IMO, six weeks between feedings of two mice is not enough. The metabolism of a BP is such that it could survive on that schedule, but I feed my adults a large rat every 2-4 weeks, depending on the snake. I agree with Ballkingdom, switching to rats would be better, and cheaper, for you both.
You may have to scent a rat, since it is used to mice. Scenting is getting the rat to smell like a mouse, usually by obtaining some used bedding, and letting the rat sit in it for a while.
Let us know how it goes, and if you need any other help!