"OK, it looks better than original fluid before tonight's main event in the garage, but I can't see the bottom"

That's the deal with MB - you can never see the bottom - it is a bottomless pit... Seriously though, I've done this job a couple of times already and I do not think you will ever be able to see the filter through the the PS fluid. If it was a clear plastic reservoir like the brake fluid reservoir , you probably could.
MB fluid is light in color but it takes on a dark flavor in the aluminum reservoir. The actual amount of PS fluid in the system is quite small, so it sounds like you have already flushed away the years...