A very useful tool in the TVPaint Animation program is the Draw Fill tool. This tool enables you to draw a shape which is then automatically filled with the selected colour at the selected opacity level. For colouring line drawings in an animation this is an invaluable feature - and closely mimics the cel painting method used in traditional animation. In addition, the Draw Fill tool can be set to erase, so that one can quickly and easily draw areas that need to be erased.
It would be great if you would consider adding a tool like this for future versions of FlipaClip.