White in this case is Negative (-). The colored wires are the Positive (-).
The Pwrbtn# is the same as the "Power SW" on your Front Panel connectors, if you didn't already know that
Oh and the White wires aren't always the ground wires. It depends, but usually Black is negative (Ground) if you have a red wire paired with it (this is usually on the Speaker connection that has Black and Red wires).
Edit: Forgot to mention that the Green/White wire (+ P LED) is the Positive of the "PLED+" and the White wire (- P LED) is the "PLED -".
Concerning the H.D.D. LED would have the Red/White connector on the "HDLED+" and the White connector would be on the "HDLED-".
This would leave the Power SW connector left, which I mentioned above