Coloring subscripts/superscripts gets messed up

Consider the following scene:

```python
class TestColor(Scene):
def construct(self):
t = TexMobject("e_1", "^2")
t[0].set_color(RED)
self.add(t)
self.wait(1)
```

When rendered, this scene makes the 2 red, but not the 1. You can workaround the issue by splitting it in three parts and write the superscript first, but it's still an annoying bug.