I used to add color using water color over my pen and ink drawings.
But that all changed when I was taught how to work in Photoshop, 
It took me six months to understand how the program worked ; it took me another
 six months not to look like I was painting on a computer.
So the question I get asked is "why bother?";
in someways it saves me time. But what I truly like about it is that it gives 
me more freedom to play with color with out messing up the original pen and ink.
Nothing less fun then re-drawing an image that took you days to ink, and it never comes out looking as fresh. I also love to layer the color tones overlap them then blend
 I feel it gives the artwork some depth. 
Depending on the illustration I can use a few layers or many 
This one had quite a few layers with all the characters on one page it was easier to
 keep them apart then blend them together later.
I think I spent about two weeks from start to finish.   
well worth the time!
Almost done
(BTW this is version CS5)