​x
 
<!DOCTYPE html>
<html>
<head>
<script>
function color(color) {
  document.forms[0].myInput.style.background = color;
}
</script>
</head>
<body>
​
<form>
请编写一条消息：<br>
<input 
type="text" 
onkeydown="color('yellow')"
onkeyup="color('white')"
name="myInput">
</form>
​
</body>
</html>
​
​