We have a leather couch and loveseat that are sort of teal blue -- they were very high quality although now that they're 20 years old they look a bit dated. The 'wear' areas began to be rough and cracked and the colour was looking bad. I figured I had nothing to lose, so I took a cushion to the paint store and got an exact match in exterior latex (the paint guy said that was the most flexible paint -- although he was somewhat skeptical when I told him why I needed it!). Then I dipped a soft cloth in the paint and rubbed it in, round and round, and kept rubbing so that there was no 'edge' to it. It dried almost immediately because it was spread on very thinly and only really sunk in to the cracks. When I was done, it looked just like new (although still in the 80s style, unfortunately). I've done it a couple of times more -- about once a year -- and it still looks good. Of course if your couch is 'natural' this wouldn't help, but if it's dark brown or black or any other colour, you might find this helps. I was concerned when I started but figured it couldn't look worse -- and it ended up looking WAY better! Good luck.
Chris K, April 2007