There are two ways for the user to specify colors not already defined.
For local changes, there is the command \Color which takes two
arguments. The first argument is four numbers between zero and one and
specifies the intensity of cyan, magenta, yellow and black (CMYK) in
that order. The second argument is the text that should appear in the
given color. For example, suppose you want the words "this color is
pretty" to appear in a color which is 50% cyan, 85% magenta, 40% yellow
and 20% black. You would use the command
\Color{.5 .85 .4 .2}{this color is pretty}
For global color changes, there is a command \textColor which
takes one argument, the CMYK quadruple of relative color intensities.
For example, if you want the default color to be as above, then the
command
\textColor{.5 .85 .4 .2}
The text from now on will be this pretty color
will do the trick. Making a global color change in the midst of nested local colors is highly discouraged. Consequently, Dvips will give you warning message and do its best to recover by discarding the current color history.