Change loading screen background to white to make it less distracting when navigating between apps.

src/ui/views/chrome.jade

@@ -92,7 +92,7 @@ html(lang='en')
         -webkit-justify-content: center;
             -ms-flex-pack: center;
                 justify-content: center;
-        background: #5A5A5A;
+        background: #FFFFFF;
       }
 
       .kibanaWelcomeLogo {

src/ui/views/ui_app.jade

@@ -27,7 +27,6 @@ block content
       margin-top: 130px; /* 1 */
       text-align: center;
       background: #3caed2;
-      box-shadow: 0 0 2em #444444;
     }
 
     .kibanaLoader__logo {
@@ -100,7 +99,7 @@ block content
      */
     .kibanaLoadingMessage {
       font-family: "Open Sans", Helvetica, Arial, sans-serif;
-      color: white;
+      color: #8c8c8c;
       max-width: 540px;
       height: 50px; /* 1 */
       margin-top: 80px; /* 1 */