This is a non-adjustable script
it prepares line art to be colorized.
To colorize line art, the best way is to make a new transparent layer and set it to be in "multiply" mode. That's really all this does... saves you a few steps and makes it easy if you colorize a section or two at a time. (Flatten image when you get a section done, then colorize prep again... just a lot less clicking and won't forget multiply mode or whatever.)
When line art is colorized in this manner, you can use the brush (at 100% opacity, for consistency) and draw right over the black line art edges. See below:
Script-FU > Colorize Prep
Original line art
Colorize prep menu item
Open layers Dockable Dialog
Using a color brush on lineart
(color me layer)
Because the layer you are painting opn is in multiply mode,
Result
Colorize prep menu item
Open layers Dockable Dialog
Using a color brush on lineart
(color me layer)
Because the layer you are painting opn is in multiply mode,
Result
; Installation: ; This script should be placed in the user or system-wide script folder. ; ; Windows Vista/7/8) ; C:\Program Files\GIMP 2\share\gimp\2.0\scripts ; or ; C:\Users\YOUR-NAME\.gimp-2.8\scripts ; ; Windows XP ; C:\Program Files\GIMP 2\share\gimp\2.0\scripts ; or ; C:\Documents and Settings\yourname\.gimp-2.8\scripts ; ; Linux ; /home/yourname/.gimp-2.8/scripts ; or ; Linux system-wide ; /usr/share/gimp/2.0/scripts