For the area line chart, I don’t believe you can change the top line color but you can change the fill color by changing the color of the grouping:
You would not be able to apply conditional formatting to the y-axis text color. To change the text color you would need to use the theme settings and that would affect all text. This also applies to the text color of the center value in the donut chart.
For the RLS error message I recommend checking out the solution from a similar post below:
To hide visuals entirely I would check out this post:
You can use a calculated field to base your conditional formatting on: