A script to split a pdf file into color and black & white / grayscale pages, with duplex option. It makes use of external ghostscript software and pdftk (optional). Good to avoid paying for color printing those pages which only are black and white. Feel free to modify or improve.
If the graphics in the pdf are not completly grayscale, it migth be possible it detects the page as color. I will update with scripts to convert png and pdfs to grayscale if users demand it.