Vu meters on my Mcintosh MA-6500 no longer "Blue"

I don't beleieve the MA6500 uses LED's so it may be burned out bulbs which can be a challenge to change. Order a service maual and some bulbs from Mcintosh and you can do it your self if you are comfortable with a soldering iron. Also check with Audio Classics if they have a LED kit for this model. If they are all out I would say power supply or fuse.

If they are LED and if they are all out same story PS or fuse. Contact McIntosh Tech Support and they can tell you if there is a seperate fuse.

The fuse for the lights or power supply will be "inside" the unit. The fuse you see on the rear panel is the power supply fuse for the whole unit. McIntosh uses a seperate power supply for the panel lights and places it inside.
If the unit is working fine other than lights and you feel comfortable tearing into the unit, order a service manual and it will show you the exact location of the fuse, power supply and exploded view to access the bulbs. Otherwise I would take it in to the nearest dealer that is Mcintosh Certified for service.