Yeah, wendtii "red" is reddish (maybe only on the leaf underside, I don't recall), "mi oya" is a pretty maroon with textured leaves. I have flamingo, jacobsenii pink, & (I think) p'hang?, both regular & "mutated". Under lower light mine get only "pink-ish" mid rib or so. It's hard to say how big they get, mine were tiny offsets.
In a tank only 12 inches tall a 4-6 inch plant seems pretty tall, lol. In my 20 long I did like "spiral vallisnera" (NOT v.spiralis) aka "Italian val" or val. asiatica. It gets ~8-10 inches tall with spiraled leaves.
For swords, "Tropica" is smaller, 5 or 6 inch & there are some dwarf chain swords (more correctly laliopsis (?) now, I think). 2-3 inches.
Stem plants in a shallow tank can mean a LOT of trimming. If they're at all happy, they need control every week or 3.
Some lilies will get too big for your tank, dwarf red might be ok IF you trim off any leaves that shoot toward the surface. Trim any leaves that get too big or too tall