Change colour of widget sidebar title background

Hello all, I want to change the colour of the widget sidebar title background only, it is currently black and I want to change it to white. I realise the text will need changing as well which is no problem.

Themegrill support have helpfully said “Please navigate to Appearance > Customize > Global > Colors > Primary Colors and change the primary color as this would also affect the widget title background.” but obviously this will change everything!

Thanks 🙂

The page I need help with: [log in to see the link]