Adapt existing theme (dark purple)

Hi,

I absolutely love the idea of a purple theme. BUT The background colour of the excluded packages is super confusing.

Why would I want to highlight a folder that heavily, that is actually excluded?

So My question is: How can I adapt the theme to remove the background colour from the excluded folders?

So far I just found a whole lot of things about creating my own plugin - but is there an easier way to change this background colour than to create my own whole new theme?