Hey,

It seem the his comment is wrong.

https://github.com/moodle/moodle/blob/cccc00954d246448556a3e97874fc2288bdf9674/theme/boost/settings.php#L84

The value of the setting in questions gets assigned to the primary variable and not to the body-color as seen here:

https://github.com/moodle/moodle/blob/cccc00954d246448556a3e97874fc2288bdf9674/theme/boost/lib.php#L146

After asking about this on the forum it was suggested to raise an issue here, so here we are.

I did test if body-color is actually not assigned and indeed when using it, it reverts back to is default value assigned in the preset as expected.