Hi Paul,
Thanks for your prompt reply.
I'm afraid there's no "Edit" option to access the Site Styles when I'm on the search results page to check the theme - as you can see from the screen shot...
However, your information about the search results page using Lightest 1 theme helped me to point in the right direction. So although I couldn't access the Site Styles from the search results page, I've updated the navigation links colour in the Lightest 1 theme and it worked!
Thanks so much for your help again!
Michaela