Hi Mekemesh,
Yes, there is a way to change it.
These lines are not missing, they both just have the same color, I reckon.
- From the main menu choose 'Actions -> Show action list...'.
- To find the action you need fast, type into the 'Filter' lane: "theme tw" (no need to type more).
- The list should now show only one action: "Theme development: Show theme tweak/configuration window".
- When you double-click it, the 'Theme development/tweaker' window will open.
- In its filter type "MIDI editor ba" (no need to type more here as well).
- In the remaining list you'll find "MIDI editor background color (naturals)" and "MIDI editor background color (sharps/flats)".
- Click on it and the color dialog appears.
- Set the color to your taste.
Of course it's a good idea to have the MIDI editor open, so when leaving the color dialog you can immediately check what it looks like.
When yu're happy with your settings, save the theme so changes won't be lost.
HTH
-Data