This is cool! you can colour it by either... 1: Changing the colour on the colour box thing and using fillbucket. 2:Changing the colour and using pen or pencil or watercolour. 3:Shade it by using burn and make it a black and white one with a story behind it. Hope this helps!
For coloring in a drawing, I suggest using layers. Using the fill bucket doesn't always work very well and leaves spots un-colored (Which then you must fill in anyway.)
Using layers makes it much easier to color because you don't have to worry about coloring over the lines.