ColorSwatch<T> constructor
Creates a color that has a small table of related colors called a "swatch".
The primary
argument should be the 32 bit ARGB value of one of the
values in the swatch, as would be passed to the Color.new constructor
for that same color, and as is exposed by value. (This is distinct from
the key of any color in the swatch.)
Implementation
const ColorSwatch(super.primary, this._swatch);