The Negative and Solarize drawing modes
The Negative mode inverses the value of the pixels in the source image (the yellow of the sun becomes blue, the black text becomes white, etc.).
The Solarize mode gives a slightly different result than the Negative mode.
It mixes the negative of the source image with the source image itself and thus imitates the photographic solarization procedure.
Airbrush tool in Negative modeAirbrush tool in Solarize mode