I can't speak with authority about the origins of that kind of color picker, but I'm 100% sure that is not the reason. It's just for geometrical neatness. The a

I can't speak with authority about the origins of that kind of color picker, but I'm 100% sure that is not the reason. It's just for geometrical neatness. The adjacent colors at the "back" corners are not useful or relevant. Some colour wheels do not put primaries at 120% angles. The "opponent" theory of colour perception from the early 20th C, which has been essentially validated, led to this example: http://www.greynotgrey.com/blog/wp-content/uploads/2012/06/herings_color_wheel.jpg http://www.greynotgrey.com/blog/wp-content/uploads/2012/06/h...