I had both versions of the 35/2.8. The newer black/chrome lens had different color coatings, but they seemed to perform about the same. Chrome version is smaller and heavier. Black version has a more usable focus ring. Also, the black version has the front element sufficiently recessed in the barrel that a hood isn't usually needed.
I sold the black version, mostly for the sake of variety -- I have the 28/3.5 and 50/1.8 in black/chrome. It's a very good lens, and the chrome one was my first 35mm, but it doesn't see much use since I've accumulated a 35/2 UC-Hex, 35/2.8 Summaron, 35/2.5 Skopar, 35/1.2 Nokton and 40/2 M-Rokkor.
Ari