This is a prerequisite for a project aimed at creating a duotone tool in ruby. Necessary for all documents using spot colors. BTW I guess there is no reason why Prawn should not support all the remaining colorspaces that PDF offers.
Patches welcome. This isn't on the critical path but I'd be fine accepting a patch for it as long as it was reasonable. This won't get done by me though, in the foreseeable future.
I'll be happy to cook up something.
Great. If you get something together in the next few weeks, this could make it into 0.6