More contrast fx list and send list

[Equal]

Hi,

Currently I am using a slightly adjusted version from the default 5 theme. I just made some colours softer for the eyes.
The only problem that I am having is the fact that I can hardly see the empty fx list and send list slots (both master and mixer).
How can I adjust this without having to adjust the images (mcp_fxlist_empty etc.)

i.e. how do I create more contrast?
I need to adjust either the background or the boxes/slots themselves, but cannot find how to do this in the theme tweaker menu.

Screenshot:
https://ibb.co/KxCDwmK

Thanks as always!