Index: src/wp-includes/css/editor.css
===================================================================
--- src/wp-includes/css/editor.css	(revision 28442)
+++ src/wp-includes/css/editor.css	(working copy)
@@ -258,9 +258,13 @@
 }
 
 .mce-toolbar .mce-colorbutton .mce-preview {
-	margin-left: -17px;
+	margin: 0;
 	padding: 0;
-	width: 18px;
+	top: auto;
+	bottom: 2px;
+	left: 3px;
+	height: 3px;
+	width: 20px;
 }
 
 /* mce listbox */
@@ -570,6 +574,7 @@
 i.mce-i-underline,
 i.mce-i-alignjustify,
 i.mce-i-forecolor,
+i.mce-i-backcolor,
 i.mce-i-pastetext,
 i.mce-i-pasteword,
 i.mce-i-removeformat,
@@ -673,7 +678,8 @@
 	content: '\f214';
 }
 
-i.mce-i-forecolor:before {
+i.mce-i-forecolor:before,
+i.mce-i-backcolor:before {
 	content: '\f215';
 }