One of the classic headshaking questions over the years has been "How do I dye my couch?" Here's a review of a spray version of a fabric paint specifically designed for upholstered furniture:
It sounds a bit expensive:
"The stuff is kinda pricey at $12 for an 8-oz can, as of this writing. My orange chair took three cans to get complete coverage, while the more problematic blue color took four cans to get coverage that’s still a bit thin here and there. With shipping, it came out to about $40 to paint the one chair orange, and about $55 to paint the other one blue."
However, definitely a better choice than putting 800 boxes of RIT in your swimming pool and tipping the couch in.