If you want to get into customizing a site you should be using Firefox with the Firebug extension or Chrome and it’s developer tools. There are plenty of tutorials on how to use either of them to inspect the CSS rules and quickly change them to see the result. Once you have the desired result you can add/change the rule in either the Custom CSS area of Flexform Options or (my preference) using the My Custom CSS plugin.
Do you have a link to your site so we could take a look? If you can do that I can quickly give you the custom CSS rule to change the hover color.