That's a toughie! Off the top of my head I can't think of anything bright red that would keep its color in a shady location. Red is a sun color. All red Neos or Aechmeas would fade to green in the shade. Darker purpley-maroon shades would hold up better, like Werauhia sanguinolenta, Nidularium innocentii or possibly Hohenbergia rosea.

Neo. Fosperior might work too. It doesn't go completely green, but the color in shade is a dark maroon, not the rich burgundy you'd get in a brighter spot. Still a nice contrast to the greens.

Not really as big as you wanted, but what about Aech Big Stuff. Ok, the upper surfaces of the leaves are green but it is an upright plant showing off the deep burgundy undersides of the plants quite nice. The colour is also more intense in the shade than in the sun. Another one that also looks better in the shade and looses the burgundy colour when in the sun, Aech Burgundy!

Oh, hey, I just thought of one that stays pretty red: Ae. Valencia. You'd need a grouping of 3 for that sized space though.

Thanks for the suggestions, (keep 'em coming if anyone thinks up any more)! :)

Neo Bianca or Luca