You can have a go at lightening up or darkening a layout.
Open up the layout, press cntl E on the keyboard to go into design mode (or click on design then edit mode).
Then click on design and go to dx lamp creator.
You can then use the slider bars to brighten or dim the layout, the off image/background in particular is a quick way of doing that. Click on update, underneath the slider you've moved for it to apply.
It's always worth checking the layout in attract mode, to see what it now looks like. Sometimes it makes the lamps look horrible and jumpy or make the graininess stand out. In that case, you may wish to try the other sliders to get it looking better.
If you don't like what it's done and can't get it right or back to what it was, simply, close the layout and say no to saving. Of course if you like the change than hit yes.
Sometimes layouts are made dark because the pictures/flyer used are not great quality and/or quite grainy, so the darkness hides some of that.
It could also be done that way, because the layout designer, just wants to create that low light arcade/pub environment and make the lamps really stand out. I remember playing Blue Chip back in the day, in a lot of dark environments.