single place to contain Color-Name mapping. See https://sourceforge.net/p/autoplot/feature-requests/263/
decode the color, throwing a RuntimeException when the color is not parsable. Valid entries include:
return either a named color or "#" + Integer.toHexString( color.getRGB() & 0xFFFFFF)
return a map of the named colors.
return standard color for slightly masking background.
return the preferred name for the color