Here's a quick break down on how I typically color a piece. The bottom piece is the beginning, which start's off with a black and white ink that I've scanned in and adjusted the levels with Photoshop. The next step is applying a color as a fill for the whole page. In the third step, I begin to color the clothes and anything extra that the character is holding (in this case it's a guitar). After that, I color the hair in a separate level, This way when I shade, it's easier to go over the two and it's less work if I make a mistake. As you can see now, the skin of the character has been blocked out from the background, and in the next step, adding the shade to the body makes the skin tone stand out as a different color than the background (although, me and you know better). Lastly, I shade in the hair and add that Marceline, moon shaped, shine in her hair. This is one of the ways I color a lot of my doodles.
Take a gander at all the doodles I've drawn through out the month. I'll be posting sketches on building my characters, What the drawing looks like before and after color, and I might also throw some random nonsense or cool drawings from my other artsy fartsy friends and awesome people I admire.