In the threadlist.css about halfway down find this:
Code:
.threadbit .alt {
background: #f2f6f8 {vb:stylevar threadbit_background.backgroundImage} {vb:stylevar threadbit_background.backgroundRepeat} {vb:stylevar threadbit_background.backgroundPositionX}{vb:stylevar threadbit_background.backgroundPositionUnits} {vb:stylevar threadbit_background.backgroundPositionY}{vb:stylevar threadbit_background.backgroundPositionUnits};
Change #f2f6f8 to your desires.