gistfile1.py

import kivy
kivy.require('1.0.7')

from kivy.app import App
from kivy.uix.label import Label
from kivy.uix.boxlayout import BoxLayout
from kivy.properties import ListProperty
from kivy.lang import Builder

Builder.load_string('''
<LabelWithBackground>:
    canvas.before:
        Color:
            rgba: self.background_color
        Rectangle:
            pos: self.pos
            size: self.size
''')

class LabelWithBackground(Label):
    background_color = ListProperty([1., 0., 0., 1])

class LabelTest(App):
    def build(self):
        box_layout = BoxLayout()
        label_with_background = LabelWithBackground(text='Kivy rulz', font_size=98, pos=(400, 328), background_color=[1., 0., 1., 1])
        box_layout.add_widget(label_with_background)
        return box_layout

if __name__ in ('__main__', '__android__'):
    LabelTest().run()