In this video I go over how to customize the look of your MIDI notes in REAPER by loading a MIDI “colormap” file.
Colormaps are a way to assign different colors to different note pitches or velocities. By using a custom colormap, you can make your MIDI notes look more visually appealing and easier to read.
Try these colormaps
I put together a bunch of custom colormaps you can try plus instructions in here:
Make your own
Also you can try this free online tool to create your own