-webkit-tap-highlight-color: transparent; /* transparent with keyword */
-webkit-tap-highlight-color: rgba(0,0,0,0); /* transparent with rgba */
-webkit-tap-highlight-color: hsla(0,0,0,0); /* transparent with hsla */
-webkit-tap-highlight-color: #00000000; /* transparent with hex with alpha */
-webkit-tap-highlight-color: #0000; /* transparent with short hex with alpha */