Peter,
That fan plug end you showed is a "standard" PWM type and HP uses a modification of that with two ridges only on the sides of the fan plug. Every HP PWM fan I've worked with uses the same PWM standard wire order... ground/12VDC/Tacho/PWM control. The colors of the wires used to be standardized but that is no longer the case... most of HP's now are all black.
Shave off the one more central ridge and leave the one ridge on the side. Be careful... that is hard plastic and it will take a bit of work and caution to get most of that central ridge off. The one side ridge is enough to orient the plug and keep it in place on the 4-pin header.
Here's what HP case cooling PWM fan plug ends look like:
