[material_3_demo] Color picker not working since Flutter 3.26+

With the current version of the color picker, the hex codes for the colors are not calculated correctly.

<img width="228" alt="Image" src="https://github.com/user-attachments/assets/0b47189b-0ac5-4a4e-afba-897ded0316cc" />

<img width="240" alt="Image" src="https://github.com/user-attachments/assets/c04e8137-113f-4bbf-abc6-5e62fec4e298" />

The SnackBar should show and copy the correct color.