When you look at the visible spectrum you can see the narrow band of Yellow colors right between Red and Green. Likewise you can spot the narrow band of the Cyan colors right between the larger bands of Green and Blue.

Red and Green combine to form Yellow, while Green and Blue combine to form Cyan. Since Red and Blue combine to make Magenta, it would be logical to expect Magenta just between Red and Blue. The problem with this is that Orange, Yellow, Green, and Cyan, all occupy this position. In fact Green occupies the mid position between Red and Blue, and Violet, is the very narrow band on the far side of Blue.