I've listened to the white box version, and I'm a current owner of the blue box m50s. The main difference is the bass quantity on the blue box is greater, the midrange is a bit more recessed, and the treble has a nice sparkle. The white box version is more subdued in the bass department, the midrange is a bit more elevated, and the sparkle in the upper frequencies isn't as pronounced as the blue box version. It's totally possible to eq one or the other to make them sound like each other, though.
The bass on the m50s is adequate. It isn't like the bass of the bassier headphones like the Pro700MKII or the M-100, but it has a nice punch to them, and it's relatively clean sounding (the pro700mk2's sound cleaner). I've used these headphones for about 3 years, and I still say that they're some great all-rounders.