.icon-client {
	display: inline-block;
    width: auto;
    height: 250px;
}

.img-grey, .img-color {
    position: absolute;
    top: 0;
    left: 0;
}

.img-grey {
    z-index: 1;
    transition: opacity 0.3s ease;
}

.img-color {
    z-index: 0;
    opacity: 0;
    transition: opacity 0.3s ease;
}

.icon-client:hover .img-grey {
    opacity: 0;
}

.icon-client:hover .img-color {
    opacity: 1;
}