I was seeing some pretty choppy scrolling in the WP backend while using Chrome. After some digging around, I discovered it was the Fluency Admin plugin. Specifically all the rgba() calls in the fluency-custom.css.php file.
I coded up a function to merge the $custom_color variable with the transparent colors used for borders, shadows, gradients, etc. Not the most elegant hack, but it fixed my issues. You can grab the updated file here: