Set Note Color By MIDI Channel

Set the color of each note on a particular MIDI channel to the same color. This command is available in the Piano Roll editor, sub-menu of ‘View’.

I cannot find any method for choosing the color for a MIDI channel. It appears that they are simply assigned the first 16 colors of the Color palette, across the top row.

Change colors in the Piano Roll Editor in Logic Pro — Apple Support

By MIDI Channel: Colors notes to correspond with the MIDI channel.