How to set WEBVIEW2_DEFAULT_BACKGROUND_COLOR environment variable in WIN32

[irainbw]

I have a problem with a white screen flickering on the window. I learned from the documentation that setting the WEBVIEW2_DEFAULT_BACKGROUND_COLOR environment can solve the problem, but I don't know how to set it in win32. I tried _putenv_s("WEBVIEW2_DEFAULT_BACKGROUND_COLOR", "0x00000000");

But it didn't work and it still flickered.