Custom ColorTheme extension

[DasProffi]

Describe the feature

Extend the ColorTheme and overwrite its copyWith method and add an attribute warning color with appropriate defaults.

Why is this feature needed?

The flutter color theming does not have sufficient attributes for all colors that we want to use. Therefore we need an extension to the ColorScheme which is both compatible with the default flutter components and affords to add new colors without defaults.

Additional context

No response