From: "Mike Lorrey" <mlorrey@datamann.com>
> What we don't know is whether Newton was or was not one of those rare
> people with four types of color cones in their retinas. If he was, this
> could explain the seven color statement.
Probably not. People who can detect four colors (called "tetrachromates")
see two shades of what we would call "green" (near the middle of the
spectrum).
I think it is more probable that he called cyan "blue" (like the sky) and
then called the darker pure blue "indigo".
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