It already does?
The default option for Start8 is to use the OS taskbar colour for the menu. To reset it back to normal just pick the Reset to automatic colour option from the colour drop down in Start8.
By default Start8 disables translucency on the menu unlike the taskbar, but you can also either disable translucency on the taskbar from the control page, or allow the Start8 menu to use translucency unticking the disable translucency checkbox on the style page.