I have just found this very nice program called Recollored that colorizes B/W photos. I was intrigued from the examples provided by the Program’s author so I downloaded the program to give it a try. Here are my results.
I started with this Sepia toned image
Then I drew a few lines with the colors I wanted my image to have
Impressing to say the least, the results where much better than my expectations. Some parts ween’t colorized but that can be easily corrected with better brushing, keep in mind that this was my very first try using this program.
You can read more and see more examples here