The current development version (release due end of this year) has a
tpl_classes()[/m] function which gives you several useful classes. One of which is the "home" class whenever you are on the start page. Then you can style whatever you like in your userstyles by prepending each declaration with [m].home.
If you don't want to use the development version and/or can't wait for the next release, it is as simple as adding this to the class parameter of a surrounding container in your template:
<?php echo ($ID == $conf['start']) ? 'home' : '' ?>
(You might need to add a
global $ID, $conf; first, not sure right now.)