Aphantasia doesn't lack color, it lacks a place to put the color and therefore color has no relevance other than descriptive. The ball is just an imaginary object, like an uninitialized variable. I can imagine that one exists, I can imagine that it would have traits like red or blue, big or small, bouncy or not, but I don't visualize it, and those fields need to be filled in one-by-one, they aren't defaulted when I imagine a ball, and nothing changes other than the description if I change them. A ball rolling off a table is more like the lead into a physics question to me than an exercise in imagination.