See setSolidColors() in help.js
	which gets the radio button into solidColorScheme
		which is used in makeSchemeRangeSpt("bw") for "m" (monochromatic)
			which uses

The command is "color property_distancefromcenter 'bw';" where 'bw" means a gradient from black to white.
To reverse this, I manually used the command (in FirstGlance) with 'wb' instead:

color property_distancefromcenter 'wb' range X Y
can tune the grayscale, where X is the minimum and Y is the maximum. These can be factors of

{*}.property_distancefromcenter.min ( or .max)

For arbitrary colors (not used in FGiJ)

https://chemapps.stolaf.edu/jmol/docs/#colorscheme

especially under that heading

color "colorSchemeName" RANGE [min] [max]