Fill inside
The Fill Inside option is another way to color drawings through the use of TVPaint's Filled Shape tools:
This feature allows you to quickly fill an area. It is very useful when you want to fill a complex drawing with lots of fine pencil hatchings.
To do so, select the Filled Stroke tool and turn the Fill Inside option. Then, draw a circle around the area you want to fill. The red H.U.D denote the area which is about to be filled:
tip
You can use this feature on another Layer to keep you line and color work separate.