The case I was trying to show is about the background color around windows etc. being in one consistent color. Disregard the track and item colors as they are, that wasn't what I was trying to showcase (plus this is adjustable as well, I have it less saturated these days).
The notes are semitransparent because some belong to overlaid secondary tracks. This is how it actually looks when MIDI item is editable:
https://i.imgur.com/Tk97ez6.png
But that is, again, beside the point I was trying to make.