That background color is coming from http://metalmaggots.com/wp-admin/css/colors-fresh.min.css?ver=3.5.1
I will tell you a quick solution for this, but the below changes will dis-appear when the plugin got updated.
Please follow the below steps:
1. Login to your WordPress dashboard. And navigate to "Editor" under "Plugins" from the left side menu.
2. Select "Erident Custom Login and Dashboard" from the top right drop down menu. Now "erident-custom-login-and-dashboard/er-custom-login.php" page will open in an editor.
3. Press Ctrl + F and Search "<style type="text/css">"
4. Just below the line "<style type="text/css">" add the below styles.
div.updated, .login .message {
background: none !important;
}
Keep in mind that, this will overwrite when the plugin got updated. So if that happens, you need to redo the above steps again.