Whether the filter is "simple" or "simplistic", it is odd that such a
filter has not been abundantly available before.  I often wondered years
ago when I first started to understand the difference between raster and
vector graphics why something so simple (or simplistic) could not be easily
done.  It was also strange to me that I couldn't easily create a TeX
document with one set of graphics and have TeX generate two types of
output, namely color and a grayscale, depending on the value of some
parameters.

Utilities are available in abundance which can transform raster graphics
from color to grayscale, but until I created this yesterday, I have never
seen a utility that keeps the graphic in vector format (i.e., never
rasterizes it throughout the conversion) and converts it from color to
grayscale.  Until I read this thread, I guess I thought I was the only one
that desired such a tool.  I'm glad to see that at least I'm not alone.

Troy