If you want to change font color directly in your content, you can do it in Visual Editor. That applies to your blog posts, product descriptions or any other content that is written in Visual Editor. This will work just for that specific section and won’t change in general.
In default theme settings you can’t change the font color or size of elements such as headings, content in widgets, breadcrumbs, pagination, meta description below post...
In order to do that, you’ll need Custom CSS.
First you’ll need to find the right CSS class or selector: you can easily do it with Chrome web dev tools, Here is one simple video tutorial how to do that: https://www.youtube.com/watch?v=V2aAEzlvyDc
If you don't find the right selector or if you still have troubles, we can do this for you, but is is a paid customization.