It is not more easy to change just in the moi.css in the ui folder :)
And you can also change the bakground color Windows in the Window "Option" :)

"background-color:#D2DFE1" ; in something like "background-color:#AAAAAA;"
in the following line :)
.CommandBarBody
{
margin:0px;
background-color:#D2DFE1;
white-space:nowrap;
}
.SidePaneBody
{
background-color:#D2DFE1;
}