I'm not sure what the difference is but my old color head was a Dual Dichro Color Head and it was a large square unit. I haven't used it in years but I think Dual means dual function because it had lever on the side that was used to swing the dichroic filters out the light path for white light (non-filtered) printing such as for black & white prints on graded paper. The light was diffused
The yellow and magenta filters can be used for printing with variable contrast (VC) papers (same for both heads).