What color is the oort cloud?

Answer 1

Mostly black. That's because it is so far from the Sun that the Sun itself only looks like a fairly bright star, and there would be no light there to enable you to SEE anything.

And the Oort cloud is "only" a theoretical concept; we believe that something like it must exist as a source for the comets that we occasionally see, 4.6 billion years after the birth of our solar system. (Comets that come close to the Sun can't last for a million years!) So we've never actually detected anything out there, which isn't surprising - because the stuff out there is so far away that we'd have a VERY difficult time detecting it even with a telescope 100x more powerful than the Hubble.

To summarize, then, the Oort cloud is very far away, and populated (we think) by mostly small objects spread out over an enormously vast area. So what color would it be? Black.