correct initialization options for hmd, change default color of managed canvas to black

src/Cameras/XR/babylon.webXREnterExitUI.ts

@@ -58,7 +58,7 @@ module BABYLON {
                 var hmdBtn = document.createElement("button");
                 hmdBtn.style.cssText = "color: #868686; border-color: #868686; border-style: solid; margin-left: 10px; height: 50px; width: 80px; background-color: rgba(51,51,51,0.7); background-repeat:no-repeat; background-position: center; outline: none;";
                 hmdBtn.innerText = "HMD";
-                this._buttons.push({ element: hmdBtn, initializationOptions: { immersive: true } });
+                this._buttons.push({element: hmdBtn, initializationOptions: {immersive: true, outputContext: options.outputCanvasContext}});
 
                 var windowBtn = document.createElement("button");
                 windowBtn.style.cssText = hmdBtn.style.cssText;

src/Cameras/XR/babylon.webXRManagedOutputCanvas.ts

@@ -16,7 +16,7 @@ module BABYLON {
         public constructor(helper: WebXRExperienceHelper, canvas?: HTMLCanvasElement) {
             if (!canvas) {
                 canvas = document.createElement('canvas');
-                canvas.style.cssText = "position:absolute; bottom:0px;right:0px;z-index:10;width:100%;height:100%;background-color: #48989e;";
+                canvas.style.cssText = "position:absolute; bottom:0px;right:0px;z-index:10;width:100%;height:100%;background-color: #000000;";
             }
             this._setManagedOutputCanvas(canvas);
             helper.onStateChangedObservable.add((stateInfo) => {