CSS3 one-way transition?

/* transition out, on mouseup, to white, 0.5s */
input
{
  background:white;
  -webkit-transition:background 0.5s;
  -moz-transition:background 0.5s;
  -ms-transition:background 0.5s;
  -o-transition:background 0.5s;
  transition:background 0.5s;
}

/* transition in, on click, to black, 0s */
input:active
{
  background:black;
  -webkit-transition:background 0s;
  -moz-transition:background 0s;
  -ms-transition:background 0s;
  -o-transition:background 0s;
  transition:background 0s;
}

<input type="button" value="click me to see the transition effect!">