How to change placeholder color on focus?

Try this, this should work :

input::-webkit-input-placeholder {
    color: #999;
}
input:focus::-webkit-input-placeholder {
    color: red;
}

/* Firefox < 19 */
input:-moz-placeholder {
    color: #999;
}
input:focus:-moz-placeholder {
    color: red;
}

/* Firefox > 19 */
input::-moz-placeholder {
    color: #999;
}
input:focus::-moz-placeholder {
    color: red;
}

/* Internet Explorer 10 */
input:-ms-input-placeholder {
    color: #999;
}
input:focus:-ms-input-placeholder {
    color: red;
}

Here is an example : http://jsfiddle.net/XDutj/27/

This works for me:

input:focus::placeholder {
  color: blue;
}

In addition to Pranav answer I refined the code with textarea compatibility:

::-webkit-input-placeholder { color: #999; }
:-moz-placeholder { color: #999; }

:focus::-webkit-input-placeholder { color: #ccc; }
:focus:-moz-placeholder { color: #ccc; }​

The following worked for me:

input:focus::-webkit-input-placeholder
{
    color: red;
}