🙈Am I blind? How can I change the header colour on a product page - squarespace 7.1?

Site URL: https://besquared-probike.squarespace.com/

Am I blind?

I cant seem to find how to change the colour of the header on the product pages. 

I want the site header to black but the background to be white 🤞

I have done it for rest of the site by following this 

Quote

"The header will use the color theme of the first section. To change the color of the Site Title and Navigation Link, go to Design > Color. Select the color theme the first section is using, click Advanced, and change the Site Title and Navigation. "

But I cant find how to change a section colour for the product page without making the background black too.

The sites password is: besquared 

https://besquared-probike.squarespace.com/hjulsett/s35/275-carbon-logo 

here you can see the white header