The ColorReplacement element, which may occur multiple times, allows to replace a
color in the ExternalGraphic, the color specified in the OriginalColor sub-element, by
another color as a result of a recode function as defined in Interpolate .
Open Geospatial Consortium, Johann Sorel (Geomatys)
Recoding: Transformation of discrete values to any other values. This is needed
when integers have to be translated into text or, reversely, text contents into other
texts or numeric values or colors.
This function recodes values from a property or expression into corresponding values of
arbitrary type. The comparisons are performed checking for identical values.