You only need to adjust it on the original vision boards with the two dials/pots on the right side. Crickets (blue light) will self-calibrate.
To adjust the eye, first disconnect the air system and remove any paint. Fire it through to make sure the bolt does not cycle.
Put the hopper on (to prevent stray light coming down the feedtube), put a ball into the breach and leave the bolt open.
Select the middle position on the switch at the back (yes, there's a middle position!)
Rotate the eye-pot all the way to the right (clockwise)
Now rotate it back until the light on the back goes yellow.
If you have two-tone paint, repeat with the ball facing the other way - use the left-most setting if they differ.
Put the switch back to the left to set it to vision-on mode.
That's it.
To be honest though, I don't think I've ever had to touch mine... but it's useful to know how to do it