The old Win32 controls can change their background color just fine. I used these controls in VB6 (1998) and they all had background and foreground properties. It will take time for each app, but won't require a full re-write. More like a single if condition in the startup code.

For this specific case of Notepad:

https://docs.microsoft.com/en-us/windows/win32/controls/wm-c...

> If an application processes this message, the return value is a handle to a brush that the system uses to paint the background of the static control.

Discussion from 2001 referencing the 1998 MSDN documentation:

https://www.vbforums.com/showthread.php?98513-How-can-I-trig...

<Rant> People who haven't used Win32 in its hey day forget how many apps had awesome and unusual look and feel and only relate the the default Windows apps with no effort whatsoever at customization. Except the touch stuff, Win32 can do pretty much anything Metro can and probably more. </Rant>