RichSuggestBox SuggestionChosenEventArgs.Format.ForegroundColor only works if BackgroundColor is set to non-Transparent

### Describe the bug

In a `SuggestionChosen` handler, using `SuggestionChosenEventArgs.Format.ForegroundColor` to set token text color only works if a `SuggestionChosenEventArgs.Format.BackgroundColor` is set to something other than `Colors.Transparent`.

If this isn't done then the foreground color used it the default dark blue for links.

### Steps to reproduce

```text
Use a handler such as this and observe the text is not white:

private void SuggestingBox_SuggestionChosen(RichSuggestBox sender, SuggestionChosenEventArgs args)
{
if (args.Prefix == "#")
{
args.Format.ForegroundColor = Colors.White;
args.Format.Bold = FormatEffect.On;
args.DisplayText = ((SampleDataType)args.SelectedItem!).Text;
}
else
{
args.DisplayText = ((SampleEmailDataType)args.SelectedItem!).DisplayName;
}
}
```

### Expected behavior

A background color choice should not be required, although I'm unsure if this is a limitation of the RichEditBox control.

### Screenshots

_No response_

### Code Platform

- [ ] UWP
- [X] WinAppSDK / WinUI 3
- [ ] Web Assembly (WASM)
- [ ] Android
- [ ] iOS
- [ ] MacOS
- [ ] Linux / GTK

### Windows Build Number

- [ ] Windows 10 1809 (Build 17763)
- [ ] Windows 10 1903 (Build 18362)
- [ ] Windows 10 1909 (Build 18363)
- [ ] Windows 10 2004 (Build 19041)
- [ ] Windows 10 20H2 (Build 19042)
- [ ] Windows 10 21H1 (Build 19043)
- [ ] Windows 10 21H2 (Build 19044)
- [X] Windows 10 22H2 (Build 19045)
- [ ] Windows 11 21H2 (Build 22000)
- [ ] Other (specify)

### Other Windows Build number

_No response_

### App minimum and target SDK version

- [ ] Windows 10, version 1809 (Build 17763)
- [ ] Windows 10, version 1903 (Build 18362)
- [ ] Windows 10, version 1909 (Build 18363)
- [X] Windows 10, version 2004 (Build 19041)
- [ ] Windows 10, version 2104 (Build 20348)
- [ ] Windows 11, version 22H2 (Build 22000)
- [ ] Other (specify)

### Other SDK version

WASDK 1.5.240205001-preview1

### Visual Studio Version

Preview

### Visual Studio Build Number

Version 17.10.0 Preview 1.0

### Device form factor

Desktop

### Additional context

_No response_

### Help us help you

No, I'm unable to contribute a solution.

Inizia riproducendo il problema con il gestore SuggestionChosen fornito, concentrandoti su SuggestionChosenEventArgs.Format.ForegroundColor e BackgroundColor. Segui il percorso di formattazione di RichSuggestBox per determinare perché uno sfondo trasparente impedisce l’applicazione del colore di primo piano; il lavoro è completato quando il testo del token utilizza il colore di primo piano richiesto senza richiedere uno sfondo non trasparente.

Scritto dal modello di indicizzazione a partire dal testo della issue.