I just recently did the same thing using the "Thirteen" theme. If you look in the css, you should be able to find the appropriate code to change. I am a novice with css, but this is the code from the theme I am using and where I changed it. I also have a left-hand sidebar in my site. Under "hover", I changed the color of the text when hovered over, but you can also change the hover color by changing the # of the background color. Under "sidebar", I changed the text color as you see it upon logging on.
If you don't see anything labeled "sidebar" in the css, maybe look for "nav" and make the necessary changes there... :)
Hope this makes sense and that it helps.
#sidebar a:hover, #footer a:hover {
background-color: #A3963B;
color: #660033;
}
#sidebar {
color: #cc9966;
list-style-type: none;
}