a color object or vector of any of the three kinds of R color
specifications, i.e., either a color name (as listed by colors()), a
hexadecimal string of the form "#rrggbb" or "#rrggbbaa" (see rgb), or a
positive integer i meaning palette()[i].
mix_in
A single color any of the three kinds of R color
specifications, i.e., either a color name (as listed by colors()), a
hexadecimal string of the form "#rrggbb" or "#rrggbbaa" (see rgb), or a
positive integer i meaning palette()[i].
ratio
Numeric between 0 and 1. 0 will result on no mixing. 1 results
in all the colors turning to mix_in. Must be of length 1 or same length
as col.