First part’s easy enough:
<script src="https://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.6.3.min.js"> </script>
<script>
$(document).ready(function() {
$('#userInput').focus(function() {
$('#instructions').fadeOut();
});
});
</script>
<input id="userInput" type="textarea"></textarea>
<div id="instructions">Give me a text</div>
Doesn’t include color but that’s just CSS. If I understand the other part of your question, that takes a bit more coding but it’s still pretty basic. Try googling “jquery ajax callback” and you’ll see lots of examples.