Just press Alt. I had to change it due to some stuff not working with the right mouse button if it was used to change the light/dark palette.
Shadowforge update for 25 March 2020
To change from light palette to dark palette and vice versa
View all patches · Build 4817635 · Last edited 25 March 2020 – 11:40:02 UTC
by 
Wendy
Patchnotes via 
Steam Community
Loading changed files in Shadowforge Content…
Changed files in this update