Fix ColorPicker initial value issue

[AndrewKeepCoding]

Fixes #685

The color palette GridView was applying a selection even when not visible, causing the bound SelectedColor to reset unexpectedly. This change replaces the binding with code-behind value update to preserve the intended value when the palette is collapsed.

PR Type

What kind of change does this PR introduce?

• Bugfix

What is the current behavior?

When the ColorPicker's SelectedColor is bound on TwoWay mode, the bound property is updated to Transparent by the ColorPicker.

What is the new behavior?

The bound property value is respected.

PR Checklist

Please check if your PR fulfills the following requirements:

• [x] Created a feature/dev branch in your fork (vs. submitting directly from a commit on main)
• [x] Based off latest main branch of toolkit
• [x] Tested code with current supported SDKs
• [ ] New component
  • [ ] Documentation has been added
  • [ ] Sample in sample app has been added
  • [ ] Analyzers are passing for documentation and samples
  • [ ] Icon has been created (if new sample) following the Thumbnail Style Guide and templates
• [x] Tests for the changes have been added (if applicable)
• [ ] Header has been added to all new source files
• [x] Contains NO breaking changes

Other information

[AndrewKeepCoding]

Hi @Arlodotexe. I'm seeing CI build errors on this PR that didn't occur in my previous PR for the same ColorPicker control. Could these be related to the recent changes in #737?