@Diane: You shouldn’t change the the core theme files such as style.css, functions.php, index.php and so on. As these changes will be reverted back to original file when you update or upgrade the theme. So, to make the changes in CSS you can either do that from “Appearance => Theme Options => Custom CSS” or by building child theme and adding css in child theme style.css file.
You can play with the following CSS and change the color and size as per your need. Add the following CSS in “Appearance => Theme Options => Custom CSS” box.
.entry-title { color: #444; font-size: 34px; }
.entry-title a { color: #444; }