I've been getting a lot of asks in tumblr on how I color hair and my brush settings. I don't really do anything special in coloring nor have special brushes. In fact, it's just pretty simple and to prove that, here's the tut with little explanations. /sorryi'mbadatexplaining;
If in Paint SAI, you go to the lineart layer and check the button above the layer box that says "preserve opacity". It makes it so you can only change the color of the lines, nothing else, and you can happily color your lineart! just uncheck "preserve opacity" if you need to erase anything.
If you mean the ".. and color the lineart brown" thing, I have 3 answers but I only use Paint tool Sai so I don't know about the other programs ^^' . A) Make a new layer above lineart layer and click "Clipping Group". With this, you can color the lineart w/o getting a mess. B) Select your lineart layer and click "Preserve Opacity". At the same layer, you can now scribble colors on it w/o making a mess again. Hope this helps~ ^^'