Very good case for my color-neutralizer, in the color balance module of darktable. With auto-hue neutralization:
Then tweaked further to my taste:
To remove the mold, the best option I can think of is:
- Create an high-pass layer with a radius that matches the mold micelles
- Invert that layer
- Apply it in subtract mode
- Use a parametric masking centered on green
- Maybe use a brushed mask to isolate the mold from the grass