Skivee can probably answer that better than me, lox. I think Hubble images are light based images, but Hubble detects a lot of light that falls in the spectrum that human vision does not detect. The "photographs" we see are somehow colored or manipulated so that color is added to represent the light that our eyes do not see.

At least, I think it's something like that. If you look at the captions under Hubble images, there is usually something written there to indicate something of the sort has been done.