Hi Carl,
Well said, I too agree that an opaque solar cover is probably the best of all worlds since it allows the rays THROUGH as well as stop evaporationa and evaporative cooling - my entire argument though was just based on the fact that leaving a regular cover off does NOT decrease the warming effect on a pooll, rather it allows more energy to get into the water causing more heat buildup from the bottom up which is probably your best case scenario, yes, some is lost again due to evaporation etc, but in the grand scheme of things the WHOLE pool gets warmer with the cover off.
Now all this said, I'm mainly oing off my pool experiences and those i read about over the last few years (all AG), I don't read much of the IG stuff - it has no bearing on my pool, unfortunately, having an AG pool, I don't have the luxury of taking my cold water from below and mixing it in above - it stays below, (probably a whole different scenario with a whole different set of parameters giving a whole different set of results) the only mixing that occurs is on the top, so leaving the blue cover on causes a 2" warm spot on top with a 4 foot darn cold area below.
Oh, and pointing my return down to help mix things up doesn't work well with my pool, I end up with bad circulation over most of the pool...