Those getXXX() and setXXX() methods look very iffy to me. You are polluting your program space with multiple references to the same object, and it is only a matter of time before somebody changes its state elsewhere, probably without even knowing they are doing anything wrong. You need to take defensive copies of mutable objects coming into your object, and retain defensive copies of mutable objects going out of your object.
The Constants class should have all its fields marked final. Otherwise other code can readily change their identity again probably without noticing. Only make primitives and immutable reference types into public constants. I am not sure about Color, but I think it is all right as a constant.