I’ve never liked the ‘dark’ look for MIDI editing in Cubase, so it’s one of the things I always change when I set a new system up for myself.  It’s pretty easy to do – the option you need is under Preferences > User Interface > Color Schemes:

The colour I have chosen for ‘Editor Area Background’ is pretty much an off-white, as seen below:

With that, you should have a more usable editor!