gistfile1.py

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.gridlayout import GridLayout
from kivy.uix.label import Label
from kivy.properties import BooleanProperty


Builder.load_string("""
<CustomLabel>
    color: 1, .4, .4, 1

    canvas.before:
        Color:
            rgba: 1, 0, 0, 1 if self.odd else 1, 0, 1, 1
        Rectangle:
            pos: self.pos
            size: self.size

<TestWidget>
    cols: 6
""")


class CustomLabel(Label):
    odd = BooleanProperty(None)


class TestWidget(GridLayout):

    def __init__(self):
        GridLayout.__init__(self)

        odd = True
        for x in range(12):
            widget = CustomLabel(text="item %d" % x, odd=odd)
            self.add_widget(widget)
            odd = not odd


class TestApp(App):

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

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