Those paler ones have different coloured seats, I have sometimes seen them (and travelled on them) on the Brussels-Brussels Airport service instead of the more usual types on that run. I have it on reliable information that the refurbished ones have a slightly higher speed than the red ones (I heard that from someone who drove Belgian trains, I assume he meant the refurbished ones were the repainted ones).

This is where I found out about the “altered” trains http://www.facebook.com/photo.php?pid=3112548&id=568717794