Create an XColor given a PDF color operator and a set of
containing the arguments for that operator.
There are a variety of color operators available detailed in the
PDF Specification. However the most common ones are"rg" and "RG"
which are used to set the color to DeviceRGB. These operators take
three NumAtom arguments for the red, green and blue components,
each of which is a value ranging between zero and one. The upper
case operator is used to set the stroking color and the lower case
one is used to set the non-stroking color.
Other similar operators include "g" and "G" for grayscale; "k"
and "K" for CMYK; "sc" and "SC" for generic color components; "scn"
and "SCN" for generic components - possibly also including a
If these conditions are not met then an exception will be