To change the color of a font for all your posts, go into your style.css of your Theme and look in one of several places for the word color:#000 with the zeros representing the “hex” number which is the code for a specific color.
Typically, your post’s font color choices are in one of those areas. Just change it to “red” in one of those places, one at a time, and then upload the style.css file to your website’s Theme and check with your browser to see if the red colored font is in your post. If not, change it back and move to the next one. You’ll get the hang of this very soon.