make the luma conversion of a color api accessible
Sometimes we need to not only know if a color is light or dark, but also how much light/dark it is, or how far from black or white, so add a grayForColor method which returns the real value
Sometimes we need to not only know if a color is light or dark, but also how much light/dark it is, or how far from black or white, so add a grayForColor method which returns the real value