Minor Description
According to this documentation (and other places): https://www.w3schools.com/css/css_colors_hex.asp
there is a further 3 hex digit form of color available, namely #rgb, where each is in the range of 0-f, which expands to #rrggbb (a six-digit value with both digits of each value being the same). Thus, #fff -> #ffffff, #111 -> #111111, #123 -> #112233, etc.
The only place that needs changing would be GraphicsUtilities.decodeColor, as all other places eventually call this one method.