kivy/examples/widgets/label_with_markup.py

from kivy.app import App
from kivy.lang import Builder

root = Builder.load_string('''
Label:
    text:
        ('[b]Hello[/b] [color=ff0099]World[/color]\\n'
        '[color=ff0099]Hello[/color] [b]World[/b]\\n'
        '[b]Hello[/b] [color=ff0099]World[/color]')
    markup: True
    font_size: '64pt'
''')


class LabelWithMarkup(App):
    def build(self):
        return root

if __name__ == '__main__':
    LabelWithMarkup().run()