if you want to change only the colour of the flag on hover use this:
http://jsfiddle.net/uvamhedx/
.fa-flag:hover {
color: red;
}<link href="https://maxcdn.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css" rel="stylesheet"/>
<i class="fa fa-flag fa-3x"></i>