Caching problem after template change - Joomla! Forum - community, help and support

one of sites has had colour scheme changed blue purple after company rebranding, top banner includes menu built match specific section menus in joomla animated flash file, section menus under the banner conventional joomla menus .
i copied original template , modified css , associated images new colour scheme , saved different name, site template switched new version , modified external flash banners uploaded overwrite originals.

there seems caching problem on clients pc’s , although many of tests did perfect of pc’s client uses in offices , on, tablets, mobiles etc showing either old blue versions , or mixture of blue banners , purple menus etc.
obviously caching problem on client browser if clear history ok, worried customers not know this.
so looking try , force refresh , have tried clearing , purging cache within joomla admin , putting following script index.php try , force revalidation far no luck. have never experienced before , @ bit of loss hence post.
any ideas anyone?

<?
//set no caching
header("expires: mon, 26 jul 1997 05:00:00 gmt");
header("last-modified: " . gmdate("d, d m y h:i:s") . " gmt");
header("cache-control: no-store, no-cache, must-revalidate");
header("cache-control: post-check=0, pre-check=0", false);
header("pragma: no-cache");
?>