try this man i am sure it will works good:
this is the javascript functions :
<script type="text/javascript">
var previoustxt;
function changetxt(el) {
var s = el.style;
previoustxt = el.value;
el.value = 'Blue';
}
function restoretxt(el) {
el.value = previoustxt;
}
</script>
and this is the button :
<asp:button id="btnSearch" runat="server" backcolor="#800000" font-bold="True" font-names="Arial" xmlns:asp="#unknown">
onmouseover="changetxt(this);" onmouseout="restoretxt(this);" ForeColor="White" Height="28px" Text="Search Jobz"
Width="117px" /></asp:button>
best regards
rate if it helps you