Many times my ball pythons eat in complete darkness ... zero light ... and they do fine ... "color" doesn't matter ... it's a keepers crutch ... more than likely, the "smell" is different than your snake is used to ... sometimes it's not unusual for a ball python to go off feed when a change (such as food source) occurs.

If you go get a black rat from your previous rodent supplier, it just may work, but not because of the color.

-adam