How do I change the color of the loading background for an header/image section?

Site URL: https://www.homespunchildhood.com/language-arts

There is a flash of color (my light color in the color palette) while the heading images load. I'm assuming it is site wide, because changing the background color in the sections doesn't make a difference. I would like to change the color to white, my lightest color setting. 

*My site is still under construction, password is dogs

ETA - it's not just the section background color. It appears to be the site background color? When you scroll past header or footer, the light color appears. I want it to be white, my lightest color

Try adding to Design > Custom CSS

body, .page-section {
    background: red !important;
}

I tried this and it didn't work. Site is aussie-audio.com It appears to only happen when pictures are used as a background while they are loading in. On my site it is bright red and very distracting