This is for Gimp:
For the most basic of color maps, which add a shade of a color to your image, all you need to do is to create a new slide of the desired color and then change setting from 'Normal' to 'Overlay'.
If you want a particular color in a particular area and another elsewhere, use the gradient tool and then, after you apply your desired gradients to a transparent image, change the slide type to Overlay.
There, you have it. Pretty simple actually