Email header color

In the email notifications (such as Let’s get started) the header background color is 2295FF. How do you change that? I’ve checked my theme and that color isn’t used anywhere. I checked the LifterLMS settings and there doesn’t seem to be any option to change colors in the notifications section. I also checked the template and it says style=”background:get_css( ‘heading-background-color’ ); ?> but I’ve no idea where to set this color.