Talame wrote:I put all the layers onto 'multiply', which allowed the lines to remain clear Before that, it was very very messy
Yes, that works very well. I use the multiply/overlay technique frequently.
The only alternative to that technique is to somehow remove the 'white' areas from the line drawing so that it can be the top layer and then paint layers underneath it. I used to struggle with this, because with a scanned drawing, there's so much crud/antialiasing that goofs up the lines. Then, I found a good trick in a book...
In Photoshop, if you use the Unsharp Mask filter on the line drawing, you can get crisp lines. For settings, I generally use Amount 500, Spread(?) 15, and Threshold between 2-55. After this, I select and delete the white areas using the Select Color Range tool. If there are any 'grey spots' still existing after this, I lock the transparency of the layer and fill it with black. (or you could change it to any color).
Hope this tip helps in future projects.