Nintendo may have called the purple version of the Gamecube Indigo, but Indigo is a dark blue dye derived from a plant, unless you think your blue jeans match your GameCube
They're just names for arbitrary divisions of the spectrum of vibrating matter around us. The HN top bar is still orange even if it's not the same color as the fruit. My GameCube is close enough to the color of the dye that I'll allow it. It's also a long way from purple.
I'm talking about my actual GameCube sitting in my game storage drawer, which I checked before making that comment. That image is much brighter and much more purple than the real thing I had in my hands.
Not entirely arbitrary - some of these colors(single-frequencies) match fairly well what one of our types of cone cells can easily detect, and some don't. Some frequencies are well-detected by two of the types of cones not just one, providing us with better ability to discriminate amongst those frequencies.