MDDialog hover state change disregards custom md_bg_color

[ddauer]

When opening a simple dialog with a custom md_bg_color, a mouse exit will kill the md_bg_color (by setting it to transparent or something).

MDDialog(            
	MDDialogContentContainer(
		MDIcon(icon="weight")
	),
   	theme_bg_color = "Custom",
	md_bg_color = "red",
).open()

This is due to

KivyMD/kivymd/uix/card/card.py

Line 682 in cfe5aac

self.md_bg_color = self._bg_color

Disable this line, and the md_bg_color will stay red onMouseOut (as expected)

[cdavidson-project-canary]

This sounds similar to the bug i wrote yesterday: #1681. However, I only experienced issues with the bg color when using the @mainthread decorator.