OK, the resuts are in on my inadvertant test on the effects of an overnight delay between mash and boil. My intent on brew day was to split the runnings from a single mash into two boils. ("Why?" you may ask. I was intending to test for any effect on taste when using a counterflow chiller vs. an immersion chiller as the result of a conversation on another forum. There was no intent to wait overnight for one boil at the outset, but the brew day was a disaster...) I don't perform a mash out when I brew and I did not heat the wort beyond the mash temp before putting up for the night, nor was the wort insulated. I essentially used my keggle as a lauter grant to accumulate the runnings, mixed thoroughly, ran off half into another smaller kettle, and then executed one boil immediately to make Hop You Now. I covered the keggle with the remaining wort with Saran Wrap and moved it inside overnight. The next morning I performed the exact same boil to make Hop You Later.
Some vital stats:
Hop You Now - O.G. 1.062, F.G. 1.008 (CFC if you care)
Hop You Later - O.G. 1.059, F.G. 1.009 (IC)
So I don't think fermentability was affected by the overnight delay. While bottling yesterday, I took samples of both and my wife poured me a double-blind triangle test. I was able to correctly identify both the two samples that were the same and which batch they came from, but... Hop You Now was noticeably darker than Hop You Later, so I'm pretty sure that that biased my result. So I did another double-blind triangle test but this time in opaque glasses (does that make this triple-blind?). In this arrangement I was unable to separate the two batches.
Unfortunately, I have no idea why one would be darker than the other. Maybe something to do with settling overnight, but my keggle has a dip tube that leaves almost nothing behind when I drain it, so I wouldn't think so.