ColorPicker throws InvalidCastException when setting a default color

[timunie]

Describe the bug

The new ColorPicker throws InvalidCastException("Cannot convert the given input to a valid color") on startup

Steps to reproduce

In the demo App set a default color in the ColorPicker-Example

<mah:ColorPicker mah:TextBoxHelper.AutoWatermark="True"
                    mah:TextBoxHelper.ClearTextButton="True"
                    mah:TextBoxHelper.UseFloatingWatermark="True"
                    mah:TextBoxHelper.Watermark="Select a color"
                    DefaultColor="Blue"
                    SelectedColor="{Binding ElementName=ColorCanvasExample, Path=SelectedColor}" />

Expected behavior

The ColorPicker should respect the default color

Actual behavior

Environment

MahApps.Metro version: v2.4.0
Windows build number: Win10 19042 [Version 10.0.18363.836]
Visual Studio: 2019 16.8.2
Target Framework: .Net Core 3.1 (v4.5.2, v4.7.2)

Screenshots