You can turn your Restore light on anytime while your Routine is playing. Just tap the brightness up button quickly to make small changes, or press and hold for bigger adjustments.
The color that displays will depend on what step of your Routine is playing -- and how you have customized that step. For example, if you tap the brightness up button while the default "Sleep" step of your Routine is playing, a soft, muted red color will display. You can select any color though. Learn more about customizing your Routine here.