Formats a color as RGB, carrying its symbolic origin when it has one — #000000 (dk1).
Parameters
color: IColor|null|undefined
Returns string|null
Remarks
A theme slot, an indexed color or a tint is not a color: an audit cannot compare dk1 to
#000000 without resolving it. The origin is kept alongside because a themed color and a
literal one that happen to match are different authoring decisions.
Formats a color as RGB, carrying its symbolic origin when it has one —
#000000 (dk1).