bug: iOS style fade header color missmatch

### Prerequisites

- [x] I have read the [Contributing Guidelines](https://github.com/ionic-team/ionic-framework/blob/main/docs/CONTRIBUTING.md#creating-an-issue).
- [x] I agree to follow the [Code of Conduct](https://ionicframework.com/code-of-conduct).
- [x] I have searched for [existing issues](https://github.com/ionic-team/ionic-framework/issues) that already report this problem, without success.

### Ionic Framework Version

v8.x

### Current Behavior

When using iOS style and fade headers in a modal dialog the fade header no longer matches the content color when the ion-content has `color="light"`

This behaviour is present since Version 8.7.1:

For some modals I was able to fix this issue with setting the color on the ion-toolbar but for sheet-modals I didn't found a solution.

### Expected Behavior

Before version 8.7.1 the fade header color would match the `ion-content` color:

Screenshot taken with version 8.7.0:

### Steps to Reproduce

Basic modal setup which produces the error with ionic Version >=8.7.1:
```html

Settings




```

### Code Reproduction URL

https://stackblitz.com/edit/xyvcuvsv?file=src%2Fcomponents%2FExample.vue

### Ionic Info

```
Ionic:

Ionic CLI : 7.2.0 (/opt/homebrew/lib/node_modules/@ionic/cli)
Ionic Framework : @ionic/vue 8.7.1

Utility:

cordova-res : not installed globally
native-run : 2.0.3

System:

NodeJS : v22.14.0 (/Users/dbegnis/.nvm/versions/node/v22.14.0/bin/node)
npm : 10.9.2
OS : macOS Unknown

───────────────────────────────────────────────

Ionic CLI update available: 7.2.0 → 7.2.1
Run npm i -g @ionic/cli to update

───────────────────────────────────────────────

```

### Additional Information

_No response_

Start with the linked StackBlitz reproduction and compare the modal fade header behavior between Ionic 8.7.0 and 8.7.1. Trace the iOS-style ion-header collapse="fade" behavior with ion-content color="light" in the modal, then verify that the fade header matches the content color for both regular and sheet modals.

由索引模型根据 Issue 内容生成。