.social-image img {
    width: 170px;
    -webkit-filter: grayscale(100%); /* Safari 6.0 - 9.0 */
    filter: grayscale(100%);
    -webkit-transition: all .2s ease-in-out;
    -o-transition: all .2s ease-in-out;
    transition: all .2s ease-in-out;
}

.social-image img:hover {
    -webkit-filter: grayscale(0%);
    filter: grayscale(0%);
}