How do I change the colors of the tracks?

Whenever I import a midi, the tracks automatically get colored differently, but I can’t find where I can change them manually. For context, I use the free version.

This feature is not supported. If you are using the Pro version, then try using the script written by this coder:
Synthesizer Vでトラック色を変更するスクリプト / Track Color Changer for Synthesizer V (