Jason Ku mentioned he didn't see what new information provided the two colored symbol (the two colored circle at the begining of many diagrams). Andrew Hans replied it helped him know the color of each side when the steps aren't drawn in two colors. I would like to add the exact opposite. I've seen many diagrams with steps with two shades of grey despite the fact that the model isn't two-colored. Diagrammers do this to help folders understand better each step despite the fact that the model looks better with just one color. That circle indicates me that the model really is two-colored. And I personally like the use of a completely white circle divided in half when the model should be folded with paper that has the same color on both sides. Know what I mean?
I've seen the two-colored symbol accompanied by words. That can also be useeful. They usually tell you which parts of the model will have one color and which will have the other color. That way I can carefuly chose my paper and which of the colors I want for each set of parts That's why personally consider it an important symbol : )
