Transparent underline changes label to transparent

### Current behaviour

When activeUnderline (or activeOutline) is set to transparent, the label turns transparent as well.

### Expected behaviour

The label should use the theme color.

### Code sample

[Link to snack](https://snack.expo.dev/@p-syche/textinput-transparent-underline) with a repro.

### Your Environment

| software | version
| --------------------- | -------
| ios or android | Android 10
| react-native | 0.66.3
| react-native-paper | 4.10.1
| node | 14.18.1
| npm | 8.1.4
| expo | 43.0.3
| react-native-vector-icons | 9.0.0

### Shoutouts

This issue was discovered by @r6rob and described in a [comment](https://github.com/callstack/react-native-paper/pull/1797#issuecomment-978731341) to the PR introducing custom underline color, by @belgamo .

Start with the linked Expo Snack to reproduce the issue, then trace the React Native Paper component handling activeUnderline and activeOutline. Verify that setting either prop to transparent leaves the label using the theme color, and confirm the behavior on the reported Android setup.

Rédigé par le modèle d'indexation à partir du texte de l'issue.