Restoring color to paving stones?

About 10 years ago we put in a very large patio of multi-colored paving stones that looked like bricks. Their color has faded except for one spot where we had mats last summer. What is the best way to restore the color of the other stones? Or clean them? They seem to have moss or mildew imbedded in them, but they also look dirty next to the patch where the mats were.