Minecraft wiki entry for Map_item_format, associated text: Each base color above has 4 associated map colors below. The conversion works by multiplying each of the red, green, and blue values by a value and then dividing by 255, finally rounding down to a whole number. As of 1.8.1-pre1, the fourth base color variant is now multiplied by 135, providing a darker set of colors rather than just a clone of the second base color variant.