XmSetColorCalculation(3) on Linux
The text 59b76b34f746, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A function to set the procedure used for default color calculation "XmSetColorCalculation" "Color functions" "XmSetColorCalculation"