[Repost] DisplayPort HDMI Colour Problems

This is a repost from the MacBook Pro forums - hoping someone here might be able to help 🙂

I've got a late 2011 MacBook Pro (with the Radeon 6770M card). When certain conditions are met:

1. The machine is booted with the lid closed (it sits in a BookArc stand);

2. It is connected to an external display via the DisplayPort connector to an HDMI display;

3. It is booted into Windows under Boot Camp; and

4. The laptop lid is opened after boot.

...then the colour goes all... screwy. Here's what I mean. First picture is what the display colour should look like (as shown on the external monitor). Second picture is what it looks like on the MBP's inbuilt screen.

This is driving me bananas. I've tried a couple of different things:

1. Boot Camp 4.0 drivers;

2. Boot Camp 4.1 drivers;

2a. Boot Camp 5.0 drivers;

3. A different monitor cable;

4. A different external monitor;

5. A complete rebuild of OS X and Windows;

6. AMD native beta drivers (13.5).

Nothing's fixed it. I used to have a similar MBP, but with the 6750M card and that worked fine with the same connectors/stand/monitor/etc. The workaround is to boot it with the lid open, which is kind of a pain (in a first-world-problems kind of way).

I'm guessing there's a magic setting inside either Boot Camp control panel or drivers or even Windows itself that controls how it behaves with external monitors and colour settings and stuff like that, but I can't work it out.

Help?