How Do I Go From Grayscale to Color?
Steven Stahlberg has an excellent tutorial here on the subject of going from Grayscale to Color when digitally painting:
Grayscale to Color Painting Method
http://www.androidblues.com/JealousyStepbystep/jealousystep.html
Henning Ludvigsen also has a good explanation / process shots tutorial here:
Making a painting - Basic workflow
http://www.henningludvigsen.com/wordpress/?page_id=23
Please feel free to post links to other Grayscale -> Color Painting Tutorials if you find some good ones! 
