You'd edit your style and then in the extra properties, you'd add something like below (you'd need to change the blue to your color of choice):

Code
.topicsubject:hover {
background: blue;
}
.alt-topicsubject:hover {
background: blue;
}
.new-alt-topicsubject:hover {
background: blue;
}
.new-topicsubject:hover {
background: blue;
}