use - !important - to override default black
.fa-heart:hover{_x000D_
color:red !important;_x000D_
}_x000D_
.fa-heart-o:hover{_x000D_
color:red !important;_x000D_
}
_x000D_
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css">_x000D_
_x000D_
<i class="fa fa-heart fa-2x"></i>_x000D_
<i class="fa fa-heart-o fa-2x"></i>
_x000D_