Here's how I quickly fill sketches with a flat color in CSP. Basically I use the fill tool on the outside of the sketch with "area scaling" on 3 pixels. This fills up to the sketch plus three pixels. It's much easier to use the fill tool on the blank area outside the sketch than all the detailed areas inside it. Then I control-click the layer to select it, invert the selection so the area in my sketch is selected, and delete the color fill layer and make a new one. Now I use the fill tool again only this time I choose the "refer only to editing layer" fill option which will ignore the lines of the sketch and just fill what's selected. Takes like thirty seconds.
