The quickest way to activate or de-activate Track Volume is to hit V on your keyboard. Or the longer way is to go to the View menu, click on Audio Envelopes and check Track Volume.
The 'V' key command typically shows and hides the volume envelope (assuming VP-18 is the same as 16 and earlier). Disabling the volume envelope is an automation setting. The envelopes' color can be changed in "Options> Preferences> Display".