[Jurinjo]

Art Programs & Tutorials

Disclaimer I haven't tested all of these personally and do not guarantee anything. I simply put the links there for your convenience.
GIMP

Lots of great tools. But if you're unfamiliar to digial art tools then this will give you grief in my opinion. The interface is clunky.

Open Canvas Trial
Old Open Canvas Free

I've not used it yet as the download is a zip file and you need to download another program, if you don't have it, in order to install this program.

Paint Tool SAI
PIXLR
FireAlpaca

Step 1: Save Image
Step 2: Load Image
Step 3: File > Save As > Default (MDP, so that you can pick up and edit it at will)
Step 4: Create 1-3 new layers Keep the Line Art on top. In fact you should label it so.
Step 5: Now all layers beneath will color below the lines (since the color white is by default a background color)
Step 6: After you are done coloring: File > Save As > PNG

MyPaint

This program isn't the best for coloring. But if you are making line art then this is a great program!