Many controls offer the ability to change colors like the font and background colors. You can specify colors in a couple of different ways thanks to the DashboardColor class.
You can use any of the named colors found in the .NET Color struct.
New-UDCard -BackgroundColor 'red'
You can use standard HEX color specifiers.
New-UDCard -BackgroundColor "#E82C0C"
You can also include an alpha channel value.
New-UDCard -BackgroundColor "#E82C0CFA"
You can also specify colors using an ARGB value.
New-UDCard -BackgroundColor 16777215