Allow background color to be set back to undefined

Author: willshowell

src/lib/tabs/tab-group.ts

@@ -106,13 +106,15 @@ export class MdTabGroup extends _MdTabGroupMixinBase implements CanColor {
   @Input()
   get background(): ThemePalette { return this._background; }
   set background(value: ThemePalette) {
-    if (value) {
-      let nativeElement = this._elementRef.nativeElement;
+    let nativeElement = this._elementRef.nativeElement;
+
+    this._renderer.removeClass(nativeElement, `mat-background-${this.background}`);
 
-      this._renderer.removeClass(nativeElement, `mat-background-${this.background}`);
+    if (value) {
       this._renderer.addClass(nativeElement, `mat-background-${value}`);
-      this._background = value;
     }
+
+    this._background = value;
   }
   private _background: ThemePalette;
 

src/lib/tabs/tab-nav-bar/tab-nav-bar.ts

@@ -64,13 +64,15 @@ export class MdTabNav extends _MdTabNavMixinBase implements AfterContentInit, Ca
   @Input()
   get background(): ThemePalette { return this._background; }
   set background(value: ThemePalette) {
-    if (value) {
-      let nativeElement = this._elementRef.nativeElement;
+    let nativeElement = this._elementRef.nativeElement;
+
+    this._renderer.removeClass(nativeElement, `mat-background-${this.background}`);
 
-      this._renderer.removeClass(nativeElement, `mat-background-${this.background}`);
+    if (value) {
       this._renderer.addClass(nativeElement, `mat-background-${value}`);
-      this._background = value;
     }
+
+    this._background = value;
   }
   private _background: ThemePalette;