ColorDialog fails to reset Custom Colors collection after clicking Cancel

[Syareel-Sukeri]

.NET version

.NET 10.0 SDK build: 10.0.100-preview.3.25153.9

Did it work in .NET Framework?

Yes

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

No, still repro in .NET 8.0/9.0

Issue description

Current Behavior (.NET Core):
The Custom Colors collection is not cleared after clicking Cancel.

ColorDialogCore.mp4

Expected Behavior (.NET Framework):
The Custom Colors collection reset after clicking Cancel.

ColorDialogFx.mp4

Steps to reproduce

1. Create a WinForms project in .NET Core with Button and ColorDialog added.
2. In the button’s click event, show the ColorDialog:

    private void button1_Click(object sender, EventArgs e)
    {
      colorDialog1.ShowDialog();
    }

3. Run the application and click the button to open the ColorDialog.
4. Add a custom color and click Cancel.
5. Click the button again to reopen the ColorDialog.

or using following sample app

ColorDialogCC.zip

More Info

1. The issue cannot be reproduced when a new ColorDialog is created inside the method each time. In this case, the Custom Colors reset correctly after reopening the dialog in both .NET Core and .NET Framework.

private void button1_Click(object sender, EventArgs e)
{
    using (ColorDialog colorDialog = new ColorDialog())
    {
        colorDialog.ShowDialog();
    }
}

[Philip-Wang01]

Verified the issue on latest .NET SDK 10.0.100-preview.3.25162.24 + private dlls built from the main branch of WinForms repo. The issue has been fixed that the Custom Colors collection reset after clicking Cancel.

test13067.mp4

[Olina-Zhang]

Verified this issue in the .NET 10 Preview 3 test pass build, it was fixed that the Custom Colors collection reset after clicking Cancel, same result as above.