MDButton's md_bg_color is not effective

[WangZhongDian]

version

kivymd=2.0.0
kivy=2.3

question

MDButton's md_bg_color is not effective

code

from kivy.lang import Builder

from kivymd.app import MDApp

KV = '''
MDScreen:
    MDButton:
        md_bg_color: "red"
        MDButtonIcon:
            icon: 'flag'
        MDButtonText:
            text: 'test'
'''


class Example(MDApp):
    def build(self):
        self.theme_cls.primary_palette = "Orange"
        return Builder.load_string(KV)


Example().run()

No matter how you set the background color, it won't take effect

[HeaTTheatR]

theme_bg_color: "Custom"