Super cinnamon/black pastel morphs do end up causing an all black snake, however black is also the normal ball python background color. If you pay attention to super C/BP ball pythons that also have another morph you will notice that often the background color of those snakes affects the black of the super C/BP.
There may be a darker lean to it, but I would highly doubt a super C/BP sunset would be all black, especially considering how many super C/BP with some other morph there are and with how most look very different from the standard super C/BP
I agree with this for the most part but it doesn't always work this way. I know the banana super cinnamons are far from all purple. Hopefully you're right though.