"There's something I've been meaning to share with somebody," Miyamoto says with a grin, letting us in on a secret of the development of the original Mario Bros. "One of those constraints was that because of memory limitations, the second character had to be identical to the first character in appearance. And so we looked at that and said, 'Well even if we have the same character, we could potentially change the color of the character.' But again we were limited in the color palettes – we didn't have much in the way of additional colors that we could use. And so we looked at the turtles in that game. Their heads are sort of skin-toned, their shells are green, so what we could do is we could use the color palette from the turtle on this character. And so from those technical limitations we said 'Okay. We have these two characters. They look the same, other than the fact that their colors are different. Obviously they must be twins.' From there, we decided, 'Okay, they're twins and this other character [Luigi] must be the younger brother.'"
He adds, "This ultimately is the role of a designer: How do you take those constraints and create something that's unique and then layer on a story or some kind of a background that explains why those things exist? Ultimately that's the reason that Luigi is green, but it's one of those little development anecdotes that I wanted to share and is to me an important facet of designing: how you use what could be a constraint and use that to develop something new."