What do you mean by “html editor?” Hopefully you are not going through Appearance > Editor. In general, you should not be making changes to the theme files directly. If the theme gets updated because of feature enhancements, bug fixes, or security patches, or if changes need to be made to the theme in order to accommodate changes to WordPress, then your modifications will be lost. Instead, either create a child theme or use a CSS plugin like Jetpack or Custom CSS Manager. In your case, just making changes to the CSS is all you need, so I would recommend just installing a plugin.
I would also recommend learning how to use a web debugging tool like Firebug or Chrome Developer Tools (comes built-in with Chrome). Then, all you need to do is to right-click on an object on your web page, select Inspect element, and you can see the CSS rule(s) which affect that element. You can then add your own overriding CSS through a plugin. If you don’t understand CSS, there’s a good tutorial here.
As an example, if you open up your site in Chrome, right-click on a link and select Inspect element, the DevTools window will open up at the bottom of the browser, and you’ll see a rule on the right pane that reads:
.basic a {
color: #428BCA;
}
So this is the default color for links. If you want to see the rule for hovered links, you right-click on the highlighted element on the left-pane, select Force element state > :hover and the element will act like the mouse is hovered over it. Then you’ll see the rule on the right-pane for a hovered link:
.basic a:hover {
color: #2A6496;
}
In your CSS plugin, then, you would just add an identical rule, but using whatever color value you want. #ff0000 would give you red, for example.
