I use manual correction tool a lot but not for use on photos as such. When I have an element i have made like a bit of lace or shape etc. I then do these important steps, 1. grey-scale it and then 2. increase the colour to 8 bits. Then you can use the manual correction by having the the source colour as a dark grey and the target colour as what you fancy. It will still work without grey-scaling it but not such a good colour result. I always save a version in grey-scale and then if I want a different colour I can just go into manual colour correction to get the shade i want to match what i am doing.