How to Make Line Art Colorful

I was wondering for the past month, "How can I make the lines of line art colorful like this? [link]". And then today, I got an idea, and it worked!!! So rather than working on my English paper or studying for my math test tomorrow or for my French quiz or my Chemistry test, I drew this up (I'll be up late studying tonight...). Maybe I'll make a picture with this technique at some point...

Line art found here: [link] (I do not own it). Ahh, I love Brown Cow yogurt.

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What?

Other tutorials can be found here: [link]