How to set terminal font color to opposite of background color?

I installed oh my zsh on my Mac, and used the Agnoster theme.

Then, I installed Powerline fonts, and now it looks like this:

And I found out that it is due too the font being black when it's supposed to be white.

And if I change my Mac system theme to dark from auto (which meant that it was light) it works just fine.

I want the font color to be the opposite of the background color.

This is the background color, who's black and white as you can see, and when I dragged it to the font color, it was black and white like the background color, but I needed it to be opposite to the background color, but still white and black. How can I do it?

I'm using macOS Monterey.