Pretty much what the title says, I’ve updated my backdrop plugin to version 2.0 (well, 2.0.1 because of a small issue). This version supports the WP customizer so you can see the changes as you make them.
Also in this version of some removals. Since this was re-written some thing are inevitably missing and the way it operates is different. With the old Backdrop it would apply the background to the body element, like themes do. I received a few emails from people wanting to use it to have multiple backgrounds, something that it could theoretically do, but not in practice with most themes. When I was rebuilding the plugin for 2.0 I went ahead and used a pseudo-background element. This means that the background you theme applies is still there, and your backdrop goes over it. That, along with the new options for transparency on the background color, allow you to overlay a new background over your old one.
There is a downside to this however, because the background is always on a new element that has a fixed position, it cannot scroll normally. This is overcome by faking the scroll instead. While this is fine it does have a larger performance impact that it otherwise would. I have overcome this as bast os possible by using the requestAnimationFrame() ability in javascript, the backdrop will refresh as often as the browser re-draws. Some browsers still have a big of studdering to the animation, especially IE when handling lots of alpha level transparency, but it’s mostly mitigated. Another downside is that it requires IE 10 and up.
The plugin has been updated, you should be able to get the newest version here: https://wordpress.org/plugins/backdrop/