How to change position and color of custom post image

Hi Members,

i just want to confirm if there’s any possibility to change.

When i make a custom post image, the title of the site is centered in the middle of the image and it’s white.

How can i change it to another position and color?

thanks for your support.
I’m not if you call it “post image”. I have the german version. It’s called “Beitragsbild”.

I’m sure it won’t be so complicated for you.