The character of those outside-the-negative images is a lot like "bokeh" - dependant on a whole bunch of factors. The nature of the light source (diffused (like your colour head), collimated semi-diffused, or collimated point-source) is no doubt one of them.
I have a couple of friends who have two identical Omega D5 enlargers, save and except the light sources. I should probably encourage them to experiment.
Cool, I have a D2 now but sadly won't for a VERY long time be able to set it up. It's big haha but I've got all the stuff! Even Cibichrome tubes haha