title: Reverse opposing colors
body: <p>I have a user setup where they can choose the colors of the  alerts.  the Alert is the background color on a text or button.  But the problem comes in that if they select a dark blue and we have black letters the contrast isnt enough and you cannot read it. </p>
  
  <p>I have tried to make a function to get the reverse opposing color but havent got too far.  </p>
  
  <p>Is there such a function?</p>