Access AppThemeBinding in App.xaml with C#

Hi!

I'm using AppThemeBinding to respond to the dark theme on a device. I put all the colors in App.xaml and then I using static resource to access the style:

In some pages I also have a label which changes the color to red when something is wrong. The thing here is that red on a dark background is not helping, so I decided to make this color yellow. Problem is that I don't know how to do this.

Ideally I need a code that is able to access the AppThemeBinding property in App.xaml using C#. Then I make sure that all colors are at one place and then the color gets chosen based on the light theme or dark theme.

I hope someone can help.