I'm almost finished (only the sunglasses remaining, but they're a tricky part) coloring an illustration of Sakamoto Ryoma from Nanae Chrono's Peacemaker Kurogane #4 for weblog layout (and probably wallpaper) purposes. To be frank, the hardest part (more than the coloring itself) was hand-cleaning the image from the screentones.
Tip to those who want to colour a B&W picture with screentones: Scan it at humongous size and resolution and increase the contrast so you can see every damn little dot in the pattern. Then paint over them with white.
I usually do this kind of Photoshop coloring this way:
1. Duplicate the layer with the B&W clean image, erase the background layer, and change the mode of the surviving layer to Multiply
2. Create "Normal"- mode layers as necessary so that nearby color zones are in different layers - for ease when cleaning them
3. For every zone of colour draw a quick outline with the Freeform Path tool, then holding the Control key adjust the path so that it adapts to the zone outline.
4. Change the path to a selection, fill it with the base colour. If you want airbrushed shades, this is the moment to make them.
5. Rinse, repeat.
There will be a KIRAKIRA-sparkly Ryoma wallpaper in the future, I should expect ^___^