TGWTF---It is Alternanthera reineckii "variegated." I think that some of the color is due to my specific lighting scheme, as well as a nutrient-rich substrate and a modified EI dosing regimen. I'm just able to bring out the red coloration pretty nicely using all of these factors.
Like I said above, it's a neat plant with variegation similar to Hygro polysperma "Sunset." I picked some up from JoJo about 7-8 months ago. Here it is back in my old set up a few months ago:
Thanks Kwheeler!! It's added a great touch to the set up, and helps with the humidity, too! Noticeably, in fact, which was a little surprising to me!