My S-I-L has this growing in her beds in Atlanta. It's clumping, currently maybe 14-16" tall (but thinking it will still get at least a little taller), and variegated with colors of lime-green and white/cream. It's streaked variegation, not albomarginated. The leaves also have a thicker substance to them, almost (but not quite) succulent.
She says its non-flowering, which is why I thought it may be a grass. I don't know anything about grasses, tho. She cuts it back to the ground every year (so it's a perennial), and it comes back from the roots.
Any ideas?