Cel colouring in PaintBBS
Start with a blue sketch (or similar) on layer 0.
Next, draw the outline on layer 1. I usually do a rough outline with the solid tool, 2 pixels wide, then go around it again to tidy it up and vary the line width. You can see where I started doing that on her fringe. If you want to check how the outline looks without the sketch before it's complete, select layer 0 and right click it to hide it. (It's useful sometimes, really!)
The outline is done! At this point I made a mistake. Usually I fill layer 0 with flat colour, so when I'm colouring the character I make sure I don't miss any white areas. Ah well, onwards regardless...
Before you start colouring you need to mask the outline. Masks are set for black by default. Then you can start colouring on layer 1. I do each colour one at a time, 'cos I'm lazy and like to go over the edges a bit. Use the solid tool to put down flat colours rather than the paint tool, just to make sure you get all the corners.
Next, add some shadows. I do this with the solid tool too, but don't you think it looks a bit harsh..?
You don't have to soften the edges, but it does look nice. Just go around the edges with the watercolour tool at a small size (3 or 4 pixels wide should do it).
Then, add highlights in the same way.
And finish colouring the image.
Finally, switch back to layer 0 to draw the background. All done!
Some copyright crap: All of this is © me. Steal and I shall slurp your brains through a straw. Indeed.