How to invert custom brush in GIMP

Question

Is it possible to invert a custom brush?
I am not talking about angle/rotation/horizontally but what part of the brush is drawn on the canvas.
I want to invert it in a way so the area which normally does not apply color will apply color.

Answer 1

A workaround: Paint black into a originally white layer mask. Have a new layer with white layer mask and the layer itself filled partially or fully with the new color. The layer must have alpha channel.

Answer 2

• Windows>Dockable dialogs>Brushes
• Right-click the brush, and Open brush as image (image should be grayscale)
• Color>Invert

Two ways to use the brush:

• One-time use:
  • Select>Select All
  • Edit>Copy
  • Use the clipboard brush (first in list)
• Long-term use:
  • File>Export as .GBR, in one of the directories listed by Edit>Preferences>Folders>Brushes (the one you can write into).