See Tree::show_dot.
	redef fun to_dot do
		if is_red then
			return "\"{self}\"[style=filled,fillcolor=red,fontcolor=white];\n"
		else
			return "\"{self}\"[style=filled,fillcolor=black,fontcolor=white];\n"
		end
	end
					lib/trees/rbtree.nit:138,2--145,4