Two clicks are required to change the Highlighter tool color through the Comment Tools Tab.
By allowing users to add individual colors to the Tools Tab, one could change colors with one click.

(Three clicks are necessary if you're changing the color of a highlight after highlighting: click to select highlight > click 'change color' > click to select desired color)

I - and I believe, plenty of users - color code with the Highlighter tool, yet, changing colors requires too many clicks, especially when one is changing between colors frequently. It also creates a hassle to the reading flow. Adding the suggested function may significantly mitigate this problem while also generating easier usage flow. The option for adding individual colors could be added to the already existing 'Customize Comments Tools' tab.

A more complex solution would be adding a movable tab (similar to the one existing in the new adobe), in which the user could add all their comment tools - like a pencil case - and move it around, further increasing the ease of use.