The light blue SE has the quick-set bobbin needle plate, 3 hole/position straight-stitch needle plate which makes 1/4" piecing easier, a new buttonhole foot, and I think a different spool holder.
The new straight-stitch plate is NOT backwards-compatible with the older 8900.
My Elna has the same needle plates and piecing stitches and I LOVE it for piecing.
(note - early on there was a red-faced 8900 that was either called a Special Edition or a Limited Edition. That's the one that's just cosmetically different from the standard 8900. The light blue one is an improved version)