title: how to assign color to helperText material ui to highlight error in TextField
body: <p>How to assign a color to <code>helperText</code> <strong>material-UI</strong> to highlight the error in <code>TextField</code>.I am unable to set the color to <code>helperText</code> in material-UI.</p>
  
  <p>I tried to use <code>MuiFormHelperText-root-406</code> to apply CSS 
  but it does not work</p>
  
  <pre><code>&lt;Grid item xs={3}&gt;
     &lt;TextField
         label="EmailId" 
         name="emailId" 
         value={editItem.emailId} 
         onChange={this.editInputValue} 
         helperText={this.state.emailerror}  /&gt;      
  &lt;/Grid&gt;
  
  
  .MuiFormHelperText-root-406{
     color:rgba(255,0,0,0.5);
   }
  </code></pre>