Please try this
Step 1:- Take a TextBox (Text1)
<input type="text" id="Text1" style="background-color:blue" value="Enter your text here" onfocus="show()" />
Step 2:- In the Head Part:-
<script type="text/javascript">
function show()
{
document.getElementById("Text1").value=" ";
document.getElementById("Text1").style.backgroundColor="White";
}
</script>