What if I asked you to visualize a wogembibobble rolling off a table, would you be able to visualize it, and if so would you say it has a color? And if you're curious what a wogembibobble is, all that you need to know is precisely what can be inferred from the question: it's something that's cabable of rolling, and all other variables are free. When I do this exercise, I visualize a bulbous-tentacled blobby sort of slime rolling off the table, but although I can't imagine it without giving it a shape (and even a texture, apparently), I can imagine it without giving it a color. I don't pretend to know how this works, and I assume other people will have different experiences.