更改Kivy小部件的文本部分的颜色

我正在尝试编写一个程序，如果我按一个按钮，Label小部件的一部分文本的颜色就会改变。

例如，有一个标签小部件，其文本为“ 1/0”。现在，如果我按下按钮，则1的颜色将更改为某种指定的颜色。这是我尝试过的程序：

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.button import Button
from kivy.lang import Builder
from kivy.utils import get_color_from_hex

Builder.load_string('''
#: import get_color_from_hex kivy.utils.get_color_from_hex
<b>:
    orientation: 'horizontal'
    Button:
        text: 'Press Me'
        on_press: num.text[0].color = get_color_from_hex('#04d3ff')

    Label:
        id: num
        text: '1/0'
''')

class b(BoxLayout):
    pass

class main(App):
    def build(self):
        return b()

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

这是我得到的错误：

Traceback (most recent call last):
   File "b.py", line 28, in <module>
     main().run()
   File "/usr/lib/python2.7/dist-packages/kivy/app.py", line 828, in run
     runTouchApp()
   File "/usr/lib/python2.7/dist-packages/kivy/base.py", line 487, in runTouchApp
     EventLoop.window.mainloop()
   File "/usr/lib/python2.7/dist-packages/kivy/core/window/window_sdl2.py", line 619, in mainloop
     self._mainloop()
   File "/usr/lib/python2.7/dist-packages/kivy/core/window/window_sdl2.py", line 362, in _mainloop
     EventLoop.idle()
   File "/usr/lib/python2.7/dist-packages/kivy/base.py", line 330, in idle
     self.dispatch_input()
   File "/usr/lib/python2.7/dist-packages/kivy/base.py", line 315, in dispatch_input
     post_dispatch_input(*pop(0))
   File "/usr/lib/python2.7/dist-packages/kivy/base.py", line 221, in post_dispatch_input
     listener.dispatch('on_motion', etype, me)
   File "kivy/_event.pyx", line 718, in kivy._event.EventDispatcher.dispatch (kivy/_event.c:7699)
   File "/usr/lib/python2.7/dist-packages/kivy/core/window/__init__.py", line 1030, in on_motion
     self.dispatch('on_touch_down', me)
   File "kivy/_event.pyx", line 718, in kivy._event.EventDispatcher.dispatch (kivy/_event.c:7699)
   File "/usr/lib/python2.7/dist-packages/kivy/core/window/__init__.py", line 1046, in on_touch_down
     if w.dispatch('on_touch_down', touch):
   File "kivy/_event.pyx", line 718, in kivy._event.EventDispatcher.dispatch (kivy/_event.c:7699)
   File "/usr/lib/python2.7/dist-packages/kivy/uix/widget.py", line 432, in on_touch_down
     if child.dispatch('on_touch_down', touch):
   File "kivy/_event.pyx", line 718, in kivy._event.EventDispatcher.dispatch (kivy/_event.c:7699)
   File "/usr/lib/python2.7/dist-packages/kivy/uix/behaviors/button.py", line 110, in on_touch_down
     self.dispatch('on_press')
   File "kivy/_event.pyx", line 714, in kivy._event.EventDispatcher.dispatch (kivy/_event.c:7654)
   File "kivy/_event.pyx", line 1224, in kivy._event.EventObservers.dispatch (kivy/_event.c:13497)
   File "kivy/_event.pyx", line 1108, in kivy._event.EventObservers._dispatch (kivy/_event.c:12329)
   File "/usr/lib/python2.7/dist-packages/kivy/lang.py", line 1557, in custom_callback
     exec(__kvlang__.co_value, idmap)
   File "<string>", line 7, in <module>
 AttributeError: 'str' object has no attribute 'color'

编辑：解决方案

这项修改适用于那些碰巧遇到类似情况并通过Google搜索进入此处的用户。Inclement的解决方案运行完美。这是kv语言的解决方案代码：

<b>:
    orientation: 'horizontal'
    Button:
        text: 'Press Me'
        on_press: num.text = "[color=#04d3ff]1[/color]/0"
        on_release: num.text = "[color=#ffffff]1[/color]/0"

    Label:
        id: num
        markup: True
        text: '1/0'