I am trying to remove Testor"s paint from a Spike Anodized Aluminum lower receiver and have tried Citristrip and it didn't remove all of it. What Paint Stripper is Safe on Aluminum Anodizing?

Go to local auto paint supply or NAPA and get some Fast Enamel Reducer, 3812 is the DuPont number. It will wash that paint right off and won't hurt most plastics either.

With the exception of acid, I don't know of a solvent that will harm a Type III HC anodized AR finish.

Try some denatured alcohol.  If that doesn't work, MEK.

OP, did you use an old toothbrush with the citristrip? I usually cake it on, let dry, scrape/rub the top coat of paint off, cake another layer on, let dry again, then add just a small amount to get everything liquid again before brushing with a toothbrush or nylon brush. Works every time.

If that doesn’t work, there aren’t any chemicals I know of beside strong acids and bases that will remove the oxidation layer. Typical solvents like benzene, toluene (stuff that’s in carb cleaner, or at least make up the majority of it), alcohols, water, etc have no chemical interest in the oxidized aluminum so they’re general safe to use. Mineral spirits or carb cleaner are just fine and will get the job done.

Spray on Citristrip ate the rustoleum camo paint right off this lower and didn’t hurt a thing

Bix. It will strip epoxy coat also.

Citri-Strip is my preferred paint remover.

I used the spray on aircraft stripper, Jasco maybe, didn't hurt anodizing. It will eat your latex gloves and burn your skin.
Only thing I know that removes anodizing is oven cleaner.

I've used Klean Strip aircraft paint remover to try and remove Gunkote. It's for epoxy paints, but didn't work very well on Gunkote.

Ended up blasting the finish off with aluminum oxide media. That worked great.

Klean Strip didn't hurt the aluminum at all.  Like others said, you would have to use a strong base to damage the anodizing layer.

I used Citri-Strip to strip the finish of an old,  dirty Win. model 70 stock.  It worked wonders and didn't damage the wood at all.  

I'm sure your guys' experience as a safe paint remover is spot on.