Q: Why make this in lieu of using "HSV(H, S, V)"?
A: Because XenForo color picker in XenForo 2.1.x
has limitations.
Q: Why some colors are still shown as question marks in color pickers of non-color property groups?
A: This is a bug in XenForo 2.1.0 - 2.1.9 and
is fixed in 2.1.10 release.