Since this thread has been revived once again I thought I'd mention a few things after reading through it (wow this is a long one!)
I've owned about a dozen corn x king hybrids, only 1 had a complete anal plate - all others had a split plate. Whether that means anything or not at this point ...
The few of these that have been less than 50% king were nearly unidentifiable as having any king in them. The colors were a liiiiitle bit off - slightly more yellowing. But no more "off" than they would have been if they had been Buf or Toffee.
Also, whether the original tesseras were hybrids or not, I DO believe some of the more recent ones have been "created" by breeding cali-kings to corns and selling the offspring (perhaps a few generations down, of course) as pure. I've seen many winks and nods from hybrid breeders lately, claiming that tesseras are hybrids... they "know" they're hybrids because they've made them themselves. I think some hybrid breeders are taking the opportunity (of similar looking genes) to sell their hybrids as "pure" - why? a larger market perhaps? Just to say they can? who knows.
A friend of mine recently hatched some "corns" from a tessera x tessera breeding... some were nearly completely black/white (with a touch of brown, so they weren't anerys) and many had short snouts and that small head pattern that cali kings have... as well as a very "banded" pattern compared to most corns. She was QUITE upset that I thought they were hybrids... but I was trying to be honest with her. The adults she bred did not appear cali-king in the least, though. Which seemed odd, but I imagine that kind of thing can happen when you're breeding hybrids - some offspring will look more hybrid than others, even when it skips a generation.
Regardless. As of 2019 I think there ARE cali-king newport hybrids in the hobby being sold as pure corns... whether the first ones were, we'll never really know. But be aware of who you're buying from.