using jquery with animation it's easy to do -

$(".MessageReply").click(function (e) {
e.preventDefault();

$("#<%= submitPostTextbox %>").focus();
$("#<%= submitPostTextbox %>").animate({ borderColor: 'orange' }, 500);
$("#<%= submitPostTextbox %>").animate({ borderColor: '#888' }, 10);
});

so when element with MessageReply class clicked -

this line -
$("#<%= submitPostTextbox %>").animate({ borderColor: 'orange' }, 500);
will show orange border.

Then this line -
$("#<%= submitPostTextbox %>").animate({ borderColor: '#888' }, 10);
will show default border color again.

hope it helps.don't forget to give a +1 in google search for this page.