Change colour of Bedford template banner background fade

I'm trying to figure out a way to change the background colour of the banner block in Bedford.

When a new page is loaded the template loads what appears to be a black background and quickly fades to the banner image. My client would like the background colour to be a navy that matches their colour scheme.

I'm able to change backgrounds on blocks using custom code, but can't figure out how to target this black colour.

@jhsloan Would it be possible to share your site URL? I think it can be done with custom css.