Blue is the name Physicists give to the Hue
that covers a wide range of wavelengths near the other end of the visible
spectrum. The single wavelength most often used to describe Red is
700 nanometers, Similarly; Blue has a wavelength of 400 nanometers, while
Green has a wavelength of 550 nanometers.
In Fig 1, to the right, we see three pure Hues
of color, with identical intensities, and equal saturation, in the form of
three spotlights. These are what a Physicist calls Red, Green, and Blue.
If these spotlights are moved so that they partially overlap each other, then
"White Light" is produced where all three overlap, as shown in Fig 2 on the
next page.