Taskbar changes color to default blue if I'm running dual displays

So basically, for the past year, my Thinkpad X220T with Windows 7 Home Premium 64 bit has always had a black colored taskbar with the same Aero theme, and I've never changed anything. And when I was on battery, for whatever reason, the color of the taskbar changed automatically to this default light blue color. And I've always liked that because it subconsciously reminds me I'm on battery. But no matter what happened, if I hooked up the AC, the computer would go back to its black taskbar color. Even when hooking up to my external monitor through DisplayPort, the taskbar was always black. Also, the computer uses integrated Intel HD 3000 Graphics.

So a couple days ago, something must've happened, because when I hook up the laptop to the same monitor, with the same connections, and on AC, the taskbar is the default light blue color. But when I close the laptop lid, and only use the external as the solo monitor, the taskbar changes to black. And when I disconnect the monitor plug, and only use the laptop's display, the taskbar is black. So essentially the taskbar is only light blue when outputting to both monitors at the same time.

At this point, I manually update some drivers through lenovo site. Nothing.
I run System Update to update everything, including BIOS Utility, just in case I missed something. Nothing.
I go to Personalization and try to find a way to change the taskbar color, but contrary to google results, I can't find the so-called "Color Mixer" under "Window Display".
I go to Power Manager, thinking this was what initially made the color changes, but can't find anything even remotely close.
I use the product key for Windows 7 Home Premium on the laptop (legit) to update my Win7 from its pirated beginnings. Nothing.
I uninstall ThinkVantage Power Manager. Nothing. I install newest version. Nothing.

So finally I notice this weird situation:
When I'm running one display only, if I go to Personalization > Window Color, the window that opens is the Color Mixer, which is the holy grail I've been searching for all along.

When I'm running both displays at once, if I go to Personalization > Window Color, the window that opens is this one, in the attachment, and there is no Color Mixer to be found.

When I'm running dual displays, why does Win7 give me different options??

well I think I found the problem. When in dual monitors, none of the Aero options work. e.g. nothing happens when I try to use Windows key+Tab; Alt+Tab leads to an old looking version of it, circa Windows XP.

So how do I enable Aero options? When I go to Personalize, the Aero themes are listed, but if I click on one, nothing changes, with respect to my problem. Windows+Tab doesn't do anything.

Why did my graphics card all of a sudden stop supporting Aero in dual displays??

HOLY SHIT. SOLVED!

Go into Graphics properties. Change Color Depth of BOTH the internal display and external display from 16 bit to 32 bit (which is something I initially switched a few days ago, and I'm now realizing was the cause of this whole problem hehe ) and the taskbar goes back to my original black color, and the Color Mixer screen finally comes up when I'm in dual displays. So looks like Windows 7 requires 32 bit color depth on both displays to run Aero effects. Very interesting...

Glad you got it fixed.

You should now mark the entry as "solved" so people (like me LOL) don't go reading through it to discover it is fixed - there should be a green tick button at the top of the thread starter's screen.

Thanks.