seedColorOrNull
The vibrant swatch of this Palette when there is one, otherwise the dominant one.
This is kmpalette's own pick rather than a scored one, so it is the cheap answer when you want a color that is in the image rather than the color a theme would be built from.
Receiver
the Palette to pick a swatch from.
Return
The color of the vibrant or dominant swatch, or null when the palette has no swatches.