I’d like to change the colour of the main black (stripped) bar above the showcase – a lighter colour would better fit the energy of my site.
I see how I can change most colours on the site under customize, but not this one.
How might I do this?
If I understand you correctly, this is the background social networking bar? If so, go to Appearance >> Customize >> Social Networking.
From there, you can change the colours, even hide the lined overlay.