I picked up two cans of Rustoleum Painter's Touch Ultra Cover at the hardware store, and I used Moss Green as it seemed to be the closest match to the color of our umbrella. Two cans proved to be just right for us - I have a little less than 1/2 can left. You may want to pick up more, though, if your umbrella is quite faded, or if you're trying a different color.
I removed the fabric from the wooden fram by unscrewing the top and sliding the supports out of the pockets. I placed the fabric flat on the ground in our yard.
Since the paint was green, I wasn't too worried about having painted grass. If you prefer, spread your fabric onto a painter's cloth or tarp before spraying.
Next, spray your fabric evenly. I applied three coats altogether. The fabric soaked it up and dried very quickly, and it took less time than I'd thought it would.
The shade I chose ended up being a little lighter than the original, which was fine because it really evened out the color. I love the way it looks now. Since these umbrellas start at $50, I am really happy to have this one for a few more years!