Pink noise is random noise having equal energy per octave, and so having more low-frequency components than white noise. Some people use them to "break-in" their new cans. I am sure other have more/better info on Pink Noise.
As far as the HD650's feel and quality, I think they feel very comfortable. When brand-new out of the box they may clamp a bit, but it soon goes away after some use. The build quality is pretty good too, although I have heard of minor paint chipping on the headband, but I haven't had that issue.