Highlighting :: I'd have preferred to show you, but that's too much work and i'm already so lazy lol. 
1) First of all you want to use either the selection, or the laso tool, highlight the area you'd like,
2) Then you want to either say on selection or go to it, and at the bottom it will say 

• Transform
• Scale
• Free Deform
• Rotate
• Okay / Cancel

3) What you do is you hit one of the the top 4 options, then hit Okay, it doesn't matter what one you use because your not going to do one of those four things to the picture/colors 
4) Once that is done you can color all you want without worrying about the colors going over the lines.


Part One ::  
Part Two ::  

So now your done, go off and draw your own :3 
Don't worry about if your style is different, we all have different styles and different ways of drawing, mine was merely a look at how I draw, 
But! My art is always changing, i'm always trying new things, and then improving them
So i want you to go out there, and make your own peace of art, become better at this shiz then me! 

I DARE YOU