refactor: Some parts of the code still use Color() instead of MaterialTheme colors, making the theme inconsistent.

[Shermine237]

Summary:

Some parts of the code still use Color() instead of MaterialTheme colors, making the theme inconsistent.

Steps to reproduce:

Try changing the theme colors in theme.kt or style.xml and you'll see that some parts of the application remain unchanged.

Expected behaviour:

Use MaterialTheme colors for a uniform theme. This makes it easier to change themes.

Observed behaviour:

In some parts of the code, the colors are hard-coded.