How Do I Change ALL the Colors of Ubuntu 18?

I tried to customize my Ubuntu 18 desktop colors by changing all of the purple and orange (hex and RGB) values in the gdm3.css to green, but I keep seeing purple when I sign out and sign back in and I keep seeing orange highlights when I switch 'directly' between applications! What am I missing? Is there a better way to change colors in this OS? It even says "This stylesheet is generated, DO NOT EDIT" on top, but I edited it because I could not find a better suggestion online. It is especially frustrating because the colors get reverted back by distribution upgrades sometimes. Should I be exporting different color environment variables instead? What does the Linux community know about customizing GNOME that I don't?