If you haven't done them before it would be difficult. I do them once in awhile, but for me I'm used to mixing waterbase dyes to get the color almost perfect to the original. That's because I don't take them or the seats out, and I don't want to have to dye every square inch, like far underneath the seats and tight corners. You'd need to use a compressor and spray gun, airbrush will do just fine if it's got a large nozzle. Since you don't have your colors already, you probably would need to get a match-up from some place like colorplus. You send them a swatch (cut it from way underneath one of the seats) and they send you the color. It needs to be a little watered down but not too thin, in order to get all the way down the knap. Then you lightly dry with a heatgun or hair dryer, brush it in another direction and spray a second time to get complete coverage. By the time you go through all that and spend money for the supplies, you'd need to get a very nice price for your work. So for a one time shot definitely not worth it.
As an alternative, cleaning real good, then spraying with a fabric protectant can bring a little of the brightness back (unless it's my imagination!). Maybe some others have another idea.