This was basically done in a hurry, but just wanted to document it - I basically needed pdfshuffler to visually select gray pages, and use that to split a document into a "black&white" and "color" ranges.
The interaction is a bit stupid, but all I could do fast - basically, you import your pdf(s), and you ctrl-click to select your page ranges. Then there is a new button "Paste Ranges", when you click on it, you get dialog with a text field showing your selection as page ranges (i.e. 1,2,3-5,12-15). You can of course copy this textual page range, and paste it back again - the text page range is effectuated as a selection when you click on the OK button on the 'paste ranges' dialog; the Cancel button simply closes the dialog without any changes. Then there is the Invert Selection button - if you have the above 1,2,3-5,12-15 as a current selection for a 15-page document, and you click invert, you will get the inverted selection 6-11 both in the text field, and as a selection in the icon view. That's pretty much it - so you can save your ranges, and then effectuate them, and then proceed to right-click delete, and export the rest as a new document..
Thanks in any case for a great application,