Sight was Unabsorbed color that was exuded from a given presence although the mind believed it to be the filling in, the materialization, of the object's outline.
"An Apostate: Nawin of Thais"
Steven Sills
The first thing necessary is to make some arrangement whereby two beams of identical colour-that is, of the same wave-length-reach the screen, one of which passes through the transparent body to be measured, and the other Unabsorbed.
"Colour Measurement and Mixture"
W. de W. Abney