Create a new HTML file and add this code to it:
If you open up this file in your browser, you should see a nice blue colored square.
There isn't actually any magic going on here, you create the application and append it to the DOM the same way as always. The only difference is that we added a option to the "PIXI.Application". You can pass in any kind if HEX color here, just remember to prepend it with a "0x" instead of the typical "#".