That's exactly what I was thinking...
In fact, some of the lower leaves on my NOID are just like some of the solid-green leaves on your plant, and yes all the leaves are red on the backside.
In my earlier post on this NOID I speculated that it may be a Mammy sport, and now that I look a little closer the stems and petioles are almost identical to Mammy...
I have a second large pot of this same plant but without the nice red veins, and as of now I plan on planting them both out in the ground this spring to let em grow and see what they look like by the fall, as just about everything grows better in the ground than in pots...
I'll probably plant my big Mammy in the ground too - seems like I remember reading somewhere that crotons sport better in the ground than in pots...
In fact, I intend to put most of my crotons in the ground next year and overwinter most of them outside by covering them during freezing weather.
P.S. NOID isn't really a name, but rather a temporary designation with a number as in NOID #3, for NO IDentification #3, but who knows, in the World of Crotons it may catch on and stick ;-)
