I would also be interested in @flannelhead’s answer here, since module ordering is certainly not something I feel confident talking about.
I tried a couple different options:
1 & 2: Filmic, with an earlier instance of ‘rgb primaries’ to reduce blue purity, with an instance of ‘color balance rgb’ upping saturation in the highlights, masked to high blue channel. (With the module either before or after filmic)
3: Filmic “sandwiched” between two ‘rgb primaries’, as shown in Petrikas’ tutorial. (Using the first to remove blue purity, and the second to add it back).
4: Sigmoid using the new ‘custom primaries’ section in the module. (Insetting blue, rotating slightly, and using ‘recover purity’.)
To my eye, the ‘sandwich’ approach matches sigmoid the closest, but certainly a matter of taste as to how best to ‘recover’ such blues.
Image credit: @Roger.Wilco from a spooky PlayRaw thread.
Using darktable 4.5.0+893~gac2b7321d4.