Could you please provide us some visual screenshot. We tested it on our local server and typography applied successfully in the single post title. Regarding the post, footer describes in more or provide a screenshot.
The titel is Opruimen, for which font is correct, but I want to change the color.
Also, I have tried change the image captions to be in same font-size and color as body.
Tried using extra CSSclass (.wp-caption text) (after searching online) – but this has no effect.
Changing in style.css directly also has no effect..
For more typography please go to customizer->enable extra settings and enable single page and post typography, save customizer value and refresh the customizer. Now again go to customizer->single page or single post setting and you will get the typography option. From there you can set the font family and font size.
Regarding color, we will provide the solution.
Please add the below CSS Code into Additional CSS Box through customizer.