White Balance picker weird color

I have a raw file with a strong color cast induced by a filter

When I use the drop tool on the white patch to compensate for WB the whole thing becomes purple.
WB pick works fine in Lightroom, what am I doing wrong?

original:

after WB picker on white patch in RT:

after WB picker on white patch in Lr:

raw file is here

I think RT does better with more subtle casts. I’ve some green welders glass that does not take to the wb dropper at all. Best results I get is from adjusting the channel mixer, then the rgb curves. No problem with the subtle stuff like didymium. Your best result might be by creating and using dcp profiles.

dcp corrects colors, but does not set WB
I have created a dcp profile with the filter on, but nevertheless I need to set the WB

OIC… maybe a CLUT would work.