NgStyle returns: ERROR Error: Cannot find a differ supporting object '{"background-color":"blue"}' : <p>With this in my template,</p>

<pre><code>&lt;span [ngStyle]="myStyle()"&gt; HELLO &lt;/span&gt;
</code></pre>

<p>And this in my component,</p>

<pre><code>myStyle(): string {
  return '{"background-color":"blue"}'
} 
</code></pre>

<p>I'm getting </p>

<pre><code>ERROR Error: Cannot find a differ supporting object '{"background-color":"blue"}'
    at KeyValueDiffers.webpackJsonp.../../../core/@angular/core.es5.js.KeyValueDiffers.find (core.es5.js:8051)
    at NgStyle.set [as ngStyle] (common.es5.js:2441)
    at updateProp (core.es5.js:11114)
    at checkAndUpdateDirectiveInline (core.es5.js:10806)
    at checkAndUpdateNodeInline (core.es5.js:12349)
    at checkAndUpdateNode (core.es5.js:12288)
    at debugCheckAndUpdateNode (core.es5.js:13149)
    at debugCheckDirectivesFn (core.es5.js:13090)
    at Object.View_AppComponent_2.currVal_2 [as updateDirectives] (AppComponent.html:10)
    at Object.debugUpdateDirectives [as updateDirectives] (core.es5.js:13075)
View_AppComponent_2 @ AppComponent.html:10
webpackJsonp.../../../core/@angular/core.es5.js.DebugContext_.logError @ core.es5.js:13415
</code></pre>
