I'm almost certain that this question has been asked before, so I apologise for asking it again. The problem is I don't know how to search for it because I don't know what the effect I'm after is called.
Basically I want to know how to make a photo black + white except for a single colour, e.g. adjusting a photo with something green in it so that the entire photo is monochrome but the green thing stays vivid green. I'm sorry that I'm not explaining it better but hopefully somebody understands what I mean.
-matt.
