You're misinterpreting the visible spectrum with the electronic color spectrum. This is the order of the 10's capes Consider the volume of a cube: Where the Cartesian coordinates (with range x;y;z at 1;1;1) are in a Euclidean space. In the electronic color spectrum, the origin (0,0,0) is the color black; this is because there is no color contribution from Red/Green/Blue. On the other hand, 1,1,1 is white, due to full contribution from all colors. If we let X be the intensity of red, Y the intensity of blue, and Z the intensity of green, then as we fix X and Y at 0, by increasing Z, color becomes more green. If we start at 0,0,1, and end at 0,1,0, then you would get the sequence of colors as on the capes: To skip all the Calculus jargon, the 10's cape starts at Full Green, then by adding and taking away contributions from Red and Blue, we get the color order.