Midnight Passion is more metallic purple, while hum drum is all creamy goodness.
Hum-Drum Plum (I love saying that for some reason) is FREAKIN' GORGEOUS! It's such a deep, creamy, loud, perfect blue-purple, that's bright but not too bright. I love it! I wish my camera had captured the rich color a little better. So awesome. Diamond makes some kick-butt polishes for $2.00 polish!