Dar estilos a los placeholders con css

input::-webkit-input-placeholder {
    color: black;
}
input:focus::-webkit-input-placeholder {
    color: gray;
}

/* Firefox < 19 */
input:-moz-placeholder {
    color: black;
}
input:focus:-moz-placeholder {
    color: gray;
}

/* Firefox > 19 */
input::-moz-placeholder {
    color: black;
    opacity: 1;
}
input:focus::-moz-placeholder {
    color: gray;
}

/* Internet Explorer 10 */
input:-ms-input-placeholder {
    color: black;
}
input:focus:-ms-input-placeholder {
    color: gray;
}