Any acid soln will remove the bluing.
Even the weakest of them.

Common foods like ketchup & fruit juices have acetic acid in them and that will remove blued finishes.
CocaCola will remove it the same way as it has Phosphoric acid in it.
Yes they will also disolve rust for you,,but bluing is a form of rust (iron oxide) so that goes away with it as well.

So in this instance you want to get rid of the red iron oxide (red rust) and preserve the bluing.

I know the use of very fine steel wool is frowned upon now, but it's been an acceptable way for probably 100 yrs or more. Ever since extra fine steel wool has been around, when ever that came to be?

Used with very light pressure and with oil or kero, or even soapy water, the combination will remove very light rust speckleing from blued surfaces without damaging the blue.

If you do scratch the bluing doing this, you're rubbing way too hard,,more than needed to remove the rust,,and/or you're not using any or not enough oil along with it.

Rust bluing,,even the mirror bright style on Purdey and H&H shotgun bbls is accomplished with dry 0000 steel wood as a carding material for the first couple of cycles. After that plain denim or burlap are used and then flannel for carding.
Water is often used during those carding passes for lube.

Same is done on damascus finishing of bbl.
0000 Steel Wool is used under running water after the bbls are run through the etch to then remove the loosened oxide from the harder steel portion of the composite bbl matrl and yet leave it in tact on the softer iron strips and bands.

Copper or brass 'wool' also works of course. But ultra fine steel wool is not the evil product it's made out to be.
I don't know why it's gotten that bad rap lately.

..maybe people looking for a miracle fix on a rusted piece of gun metal.
There's is only so much you can do once rusting has set in after all..