Previously, we can change the background color of the SDM login screen by following the document 19280, but it does not work on 17.x. This document explains how to change it on 17.x.
In order to change the background color of the SDM login page on 17.x, update the background color under ".loginclass" instead of ".login_page" on the castyles.css file.
e.g.
[Before]
.loginclass
{
height: 100%;
width: 100%;
background-color: #FFFFFF;
}
[After]
.loginclass
{
height: 100%;
width: 100%;
background-color: #5CACEE;
}