Quite a few ways to do this, the approach will depend on how well is that color isolated in your project. Like if you have a field of yellow flowers and green leaves--yellow and green are really close, so it will be very tough to just isolate the flowers or one particular flower.
One method would be to use the keying effects---if the color is really strong, just use the Color Key effect, sample the color and adjust the tolerance and edge feather. In my first example I had to a small mask to grab a couple of stray areas. Then use the layer as a track matte for whatever layer you want to effect.
Another keying effect you could try is Extract. In my example, I look at the color channels and saw that there wasn't much green in the rose---so I played with the levels of the green channel and added an extract effect. This method would require a bit of masking after to return some of the green I extracted from other areas of the picture.
So those are a couple of methods you might want to try...here's my example project---if you want to see what I did. I'm sure there are many other ways of isolating a single color. 7691_colorselectfolder.zip
Johnny Cuevas, Editor
"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.