IOS – setting for black and white printing from iOS

The built-in AirPrint doesn't allow this sort of functionality as of iOS 4, but if you get the HP ePrint app, you should be able to do B&W printing and manage other settings. This of course only works if you have an AirPrint/ePrint HP printer, it won't work with any other printer that you've hacked to set up with AirPrint.

You need an app, like Printopia running continuously on a logged in Mac.