title: AppCompatButton 23.2.1 app:backgroundTint doesn't color the button on Android 5.0 (API 21) but works perfectly on ≤ API 19 and ≥ API 22
body: <p>This is a very confusing question since there are so much information available and we have so many versions of appcompat support library that seem to break and get fixed repeatedly.</p>
  
  <p>Even on appcompat support library 23.2.1, <code>AppCompatButton</code> attribute <code>app:backgroundTint</code> does not correctly work on Android 5.0. It works perfectly on Android 4.4 and lower and Android 5.1 and higher. Only Android 5.0 has problems with it.</p>
  
  <p>So how to have a tinted button using AppCompat support library that runs correctly on Android 5.0? </p>
  
  <p>(I will answer my own question.)</p>