I have a small tutorial for photo manipulation in Darktable. In fact I have just reproduced Snow Photo Effect following the tutorial on youtube for Photoshop,
Winter Snow Photo Effects Photoshop Tutorial
In Darktable it was easy to do since the modules in Darktable work as adjustments layers in Photoshop.
Here the result
Three simple steps we need,
- Channel mixer
- Color zones (that is a bit tricky - you will change GREEN tones but on photo it is actually BLUE one after channel mixer)
- Color balance
To make skin of the model to be looking more natural mask the model body for the modules above for your taste.
One more example (same as in tutorial on youtube)