Use "flipping ink" to exchange the colors of two inks. You can also use it to exchange the values of +foreground-ink+ and +background-ink+ . For an example of its use, see 5.6.1, Using Flipping Ink.
Summary: A flipping ink that flips +foreground-ink+ and +background-ink+ .
Arguments: ink1 ink2
Summary: Returns a design that interchanges occurrences of the two designs ink1 and ink2 .
Drawing a flipping ink over a background changes the color in the background that would have been drawn by
at that point into the color that would have been drawn by
at that point, and vice versa. The effect on any color other than the colors determined by those two inks is unspecified; however, drawing the same figure twice using the same flipping ink is guaranteed to be an "identity" operation. If either
is not solid, the consequences are unspecified. The purpose of flipping is to allow the use of
operations for temporary changes to the display.
If ink1 and ink2 are equivalent, the result can be +nowhere+.
Common Lisp Interface Manager 2.0 User's Guide - 7 Aug 2017