Sorry about it, but I think the discussion about visuals of events in the piano roll can't be over yet.
With 0513 you tweaked the display of track/item color modes. While it did increase the visibility of selection of events, there has been a regression in terms of recognizability to which track (or item) an event belongs. There seems to be steps in the brightness an event in the Piano Roll can be displayed.
Here are two tracks which differ quite a lot in terms of brightness in the TCP. Each track has an unselected note and a few CC (in secondary items, to have equal circumstances for both tracks). Can you tell which note and which CC does belong to which track?
Ok, the MIDI display in the arrange view gives it away, but that isn't of much help in real situations...
This was no problem in earlier versions of Reaper, track colors were pretty faithfully displayed on unselected notes.
Another one:
Using brightness (almost) alone to indicate selection creates a problem which the next picture shows: Similar situation with slightly tweaked brightness. Tell me real quick, which note is selected?
While this post concentrates on track/item colors and notes, I run into the same problem creating a colormap with the goal to have event channels clearly distinguishable and of course I also want to know at a glance what is selected. I can't rely on brightness, because a selected event on one channel may look exactly like an unselected event on another channel. The very slight growth when selected just doesn't do the trick enough. Finding 16 different enough colors is already almost impossible, at the moment I kinda need to find 32 of them.
TLDR: Please, try to find some additional indication for event selection, like a border, or a change in shape.