The priority of settings is not respected when calling the `Change Background Color` dialog

[yozhic]

SumatraPDF 3.7.18299 pre-release
on Windows 11 23H2

Introduction

When the FixedPageUI > WindowBgCol setting is empty, its value is inherited from the Themes > BackgroundColor setting. And once we set a value for FixedPageUI > WindowBgCol, that value takes higher priority than Themes > BackgroundColor. This seems like the obvious logic, and I hope I’m understanding it correctly.

To reproduce

1. The FixedPageUI > WindowBgCol setting is empty. Launch SumatraPDF, press Ctrl+K, and call Change Background Color.
2. A dialog box opens, and we see the value inherited from Themes > BackgroundColor. Correct. That’s how it should be.
3. Change the value, for example, to #00ff00. Check “For all PDF files.” Apply. Close SumatraPDF.
4. Launch SumatraPDF again. We see a green canvas background—correct, that’s how it should be. Open the Change Background Color dialog.

Expected behavior

Since FixedPageUI > WindowBgCol has a higher priority, we should see #00ff00 in the color field.

Actual behavior

In the color field, we see the value from Themes > BackgroundColor. And the FixedPageUI > WindowBgCol value is ignored in this dialog.