2728. Since seeing the orange square is predictable, the phenomena has been used in optical experiments. One of these experiments consists of the image of the American flag in which the red stripes are substituted with green, the white with black, and the blue is replaced with orange. One is asked to look at the odd colored flag for one minute and then to close the eyes and there in the darkness you will see a red, white and blue flag floating in the void until if slowly dissolves and fades away.
The colors the eye sees in the dark with the eyes closed are called
phosphenes, and are there when the eyes are open but they go unnoticed.
They are most noticeable at the edges of intense colors as a kind of
halo, but we ignore them because they are so faint, and tend to
disappear if we happen to notice them.
Blue will produce an orange phosphene, and not any other color; and red
will produce a green phosphene. Purple will produce a yellow phosphene.
The phosphene colors are always the complement of the color giving rise
to the after image. Yellow is said to be the complement of purple in
color theory, and red is the complement of green. The term complement is
2731. When orange is said to be the complement of blue, everyone thinks that the word complement in this context means, “Looks good with” as in “that sweater complements those shoes, and looks good with the scarf.” But that would be "compliment," with an i.