[Dark Mode] Incorrect HighlightText system color

[Camel-RD]

.NET version

10.0.1

Did it work in .NET Framework?

No

Did it work in any of the earlier releases of .NET Core or .NET 5+?

No response

Issue description

When dark color mode is enabled HighlightText system color is set to black when it probably should be white.

Steps to reproduce

Enable dark color mode set back color to Highlight and fore color to HighlightText.

[LeafShi1]

In dark mode, the Windows GetSysColor(COLOR_HIGHLIGHTTEXT) API currently returns black instead of the expected white. This indicates that the underlying system color set provided by Windows is not correctly adjusted for dark mode. Therefore, this appears to be a problem with Windows itself.

As a workaround, we can introduce a dedicated DarkModeSystemColors class in WinForms that provides the correct dark mode mappings and explicitly supplies the correct color values ​​during rendering. However, ideally, the correct and complete fix should be located in the dotnet/runtime directory, as the SystemColors.UseAlternativeColorSet property was added there, but currently, even with SystemColors.UseAlternativeColorSet = true, the runtime does not return the correct dark mode color mappings.

To fix this issue at its root, we would need to wait for the Windows team to update their dark mode color set in their comctl modernization efforts. Is that correct? @KlausLoeffelmann

[LeafShi1]

@KlausLoeffelmann According to further investigation, the UseAlternativeColorSet property is working, but the values ​​mapped in ColorTable are incorrect.

Several of the returned colors do not match the descriptions in the comments below. Following the descriptions in the comments, the above items should all return white, and the corresponding return value should be 0xFFFFFFFF.

[LeafShi1]

After reviewing the behavior carefully and validating a number of color combinations (including light mode, dark mode, and classic mode), we confirmed that:

The behavior works correctly when using the default system colors.
Once custom colors are used, the resulting contrast or highlight appearance can vary and cannot be reliably inferred by the framework.
There is unfortunately no universal or “perfect” mapping that would work for all themes or all user-defined color choices.

Given this, the current behavior is by design, and applications that override the default colors will need to handle the corresponding validation or adjustments on their side.