Mon, April 11, 2005, 02:56 PM under MobileAndEmbedded
Recently I needed to change scrollbar colors, the disabled text color and other similar items. The target is a Windows CE device (not a PPC) and I quickly found (through the control panel) the Display Properties dialog and specifically the "Appearance" tab. If you don't have a WinCE device, launch the 4.1 emulator that ships with VS.NET 2003 to check it out.

So there was my goal: to find out what it does under the covers in order to offer us changing colors of individual items (e.g. Active Title Bar color) and also the overall scheme (e.g. Brick). We start at the obvious place: *everything* on this platform is stored in the registry. Using the Remote Registry editor (that comes with eVC) we take a snapshot before and after a scheme change and then use windiff (or similar) to spot the difference. Bingo; we find a string value "Current" under HKCU that stores the scheme name and, more importantly, we find a byte array value "SysColor" under HKLM that stores the color data. Searching on MSDN proves fruitful and informative, leading us to this and this. We test out our understanding by changing some of the RGB values in the registry, flush, reset the unit and the changes take effect. Nice!

Next step is to figure out how the control panel applet applies the change on the fly. We suspect some windows message and decide to investigate further with another eVC tool, remote spy++. Every time we apply a change a WM_SYSCOLORCHANGE message is broadcast. So we try with our own app to change the registry and then broadcast the same message but no effect takes place. Wouldn't it be great if we had the source code to the OS dialog so we could see exactly what it does? But wait, I have platform builder installed on this machine, so I could locate the code and check it out! After a few hit and miss searches, I nail it down. They call an API that does both the writing to the registry and the broadcast and the on-the-fly change: SetSysColors

Note that, if you don't care about changing colors and all you need is read-only access, then the existing System.Drawing.SystemColors class fits the bill.

This has been a not so short story, leading up to providing you with a managed class that wraps all of the above. Use it in your own WinCE (not-PPC) projects for changing color themes on the fly or single element color changes.

Download the VB class here.
Get the C# version as part of the SDF (guest, guest).