You have to specify the icon you want to use in the kml file itself. When you upload a KML file, we don't manipulate it in any way. We just give it to the gmaps api and they show it. So if your KML file hasn't specified what icon should be used, then take the standard one.
Here is a question about that on stackoverflow:
stackoverflow.com/questions/4209632/kmllayer-custom-icons
I think that there should be an option in google earth to specify your marker. You can just give them then the link to the icon on your site.
Cheers,
Daniel