Light is funny stuff. What appears to be white light is actually a mix of all the colors of light that we can see. Sir Issacc Newton classified the colors of the rainbow (spectrum of visible light) as 7 distinct shades. Like the 7 Wonders of the World, 7 days of the week, and (at the time) 7 known planets, he wanted 7 colors so added Orange and Indigo to the 5 colors he originally identified. I am one of those people who cannot distinguish indigo from blue and violet, so I left it out, but kept orange as that color I can see.
These hats use 6 of the rainbow colors and white as a nod to the mixing of all the visible colors. Worked using an intarsia in the round method, with the crown decreases fading into the over all patterning of the hat, you will master this (possibly new) technique in no time!