First I sketch out the portrait in pencil on card stock. Then I scan it into the computer and colorize the lines in adobe photoshop.
Here I block out the colors on a different layer so I can click the line layer off and on at will. I continue rendering the image until the colors and value are clear without the lines.
Last of all, I make the lines visible again and finish any issues with the color. I didn't like the whole floating in space look so I added a light background just to give a bit more interest.