I would like to make a request to Launchpad however before I do so I'd like heal with explaining what I mean.
I propose that it be possible to create overlapping areas of grey objects, or black objects with less than 100% opacity create darkness relative to addition of the "blackness" of both objects.
For example an object with 20% black on top of another object with 20% black makes 40% black where they overlap and 100% black where 5 of these overlap.
I'm new to computer aided graphic design I don't feel that I have the necessary vocabulary to make a feature request. Please rephrase to or comment so that I can submit this to Launchpad.
see this topic http://www.inkscapeforum.com/viewtopic.php?f=5&t=11551 for a better understanding of what I'm trying to say.