A very quick and conveniet way to convert greyscale images to other color values is by using the “+level-colors” operator in ImageMagic. As a simple example, imagine the image below has to be converted from greyscale (black/white) to blue/yellow.
(Note: The person in the picture is Adolphe Quetelet: astronomer, statistician and sociologist. One of the very first PhD graduates of Ghent University)
The conversion can be done with the simple command below:
convert quetelet.jpg +level-colors darkblue,yellow quetelet2.png
And gives the following result:
taptoe 