if you want to change the color in client side you can use this code
$(document).ready(function () {
if ($('#chkcolor').is(':disabled'))
$('[for ="chkcolor"]').css('color', 'red');
});
<form id="form1" runat="server">
<asp:CheckBox Text="Chage color" runat="server" ID="chkcolor" Enabled="false" />
</form>