There isn’t really a way to increase color contrast betwen the key lines in Key editor. Tip from Greg in this video How to Change the Contrast in the Background of the MIDI Key Editor | Club Cubase March 1st 2022 - YouTube is only to brighten not to change contrast. If you don’t have perfect vision you would like to be able to change the color individually of the darker and brighter lines wich I believe you could in older versions of Cubase. If I missed somthing please tell me how to do this. If not please consider it in future updates.