gistfile1.py

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.tabbedpanel import TabbedPanel

Builder.load_string("""
<TabbedPanelContent>
    canvas:
        Color:
            rgba: root.parent.custom_color
        Rectangle:
            size: self.size
            pos: self.pos

<TestWidget>
    do_default_tab: False
    label1: label1
    custom_color: .4, .4, .7, 1

    Label:
        id: label1
        text: "hello"

    TabbedPanelHeader:
        id: header_one
        content: label1
""")


class TestWidget(TabbedPanel):

    def __init__(self):
        TabbedPanel.__init__(self)
        print self.content.parent

        self.bind(on_touch_down=self.print_parent)

    def print_parent(self, obj, event):
        print self.content.parent


class TestApp(App):

    def build(self):
        widget = TestWidget()
        return widget

if __name__ == "__main__":
    TestApp().run()