Two linearts.

Reference image for this tutorial:

link to bic

Ok first notice I used a very advance technique to separate the lineart from the white background (used the high resolution version).This was done using a combination of filters,curves and selections ,gona show another tutorial for that one as soon as I do it.

Link:

This actually was made by 2 different extractions:
1.- The first one is just a simple lineart with no shading.That one is very good for coloring and I copy this one and just use the fill tool (g hotkey) to fill the spaces.

2.- The second one is the shading-lineart and it goes on top with darken .It's usefull to make some additional shading but it's not good for coloring therefore we have it on top.