Hi and welcome to the site.

Steve's correct, the stripes, both over the top, and side stripes, were optional extras as part of an external styling pack. Links to both here:

OTT Stripes

Side Stripes

He's also correct that the ST500 was only cosmetically different to the standard Mk6 ST. Whilst we don't have a dedicated ST500 section, I'm sure we'll be able to help you out on here with any questions you may have.