Unfortunately, this isn't made to be easy because its a relatively complicated stylesheet from the jQuery Mobile Library:
http://www.pegasus-express.de/iv-includ ... le.min.css
You could edit that file directly, or you could overwrite the classes by adding them to admin -> settings -> mobile CSS. This would require that you know what styles to edit though, and would probably require that you use a CSS debugger in a browser. Not something we can currently support or recommend because of the technical nature.
There is in fact a blue theme in the mobile version that we dont officially support currently. You may want to try it by following these steps:
iv-includes/templates/mobile/layout.phtml, line 27
$jqueryMobileTheme = 'b'; $textColor = 'white';
iv-includes/templates/mobile/index.html.phtml, line 31
$jqueryMobileTheme = 'b'; $textColor = 'white';
It should come out something like this:
This is a hack and there will probably be some issues, but if you want it blue, it might be worth checking out.