Hello

To change the color of the header on scroll, please attach the below given CSS by going to Admin Panel > Appearance > Customize > Additional CSS

.menu-sticky #masthead.nav-shrink {
    background-color: #588cb9;
}

Also, to change the footer color, please attach the below given CSS

#colophon {
    background-color: #384e63;
}

Hope this helps.

For any further query/confusion, feel free to reach back to us.

Regards!