Did you try overriding the default by using the Admin > Appearance > Customize CSS editor? It's a bit tricky to identify exactly the element selector that needs targeted ('Inspect element' tools are your friend), but once you do you can add the overriding CSS rules there pretty easily.
In this case, if I understand you correctly, you just want to override the background colors with your own background image, which should be pretty easy since bg images sit on top of the color. For example, if it was class .TagHero--colored (just a guess), then you might try:
.TagHero--colored {
background-image: url (path/to/your/file.tld);
background-size: contain;
background-repeat: no-repeat;
}
You'll probably need to fiddle with it but at least give it a try.
