I was going to re-use an empty gal can of Ace Hardware VM&P Naptha that I had just used up . I was rinsing it out and happened to look inside , I was quite surprised to find that there was a fair bit of what looked like rust on the bottom and side seams .
I got a flashlight and checked the other four brand new containers I just purchased and two of the four are rusted as well . I am not sure if this creates the mystery red color extract some people are experiencing or not .

So this begs the question , is this still safe to use ?

I've got the mystery red with a clear solvent from a clear bottle.

I think the redness is caused by to high a pH solution coming into contact with the bark for excessive amounts of time. That's in my experience anyway.

SWIM once left his can of naphtha in the same container as a jug of HCl...bad idea! He stopped using either one at all for a good deal of time, and the next ime he checked it, a hole had form near the bottom of the can, drained most of it, and warped the bottom of the plastic container they were both kept in. Afterwards he always transferred such solvents to hdpe jugs whenever possible. SWIM would recommend getting away from naphtha in general, but he would imagine that it could be filtered...get some more opinions on the matter though.

I have pulled from months old Mimosa/lye mix (pH > 13.5) with naptha with no contaminant - it must be something else. I even have a mix from ---- must be at least 10 months ago, I was keeping it to extract jungle. I will do a small pull with heated naptha to see if there is any redness.

My personal thoughts are that its the type of naptha i.e heavy 'with added toluene' etc or old bark that has oxidised/degraded giving rise to a new chemical. I have even thought that the farmers might be adding a colourant to the bark (highly unlikely but people do strange things for money).

A strange conundrum !!!!

Now you mention it I have only got these results when using heavy naphtha. It was a low odour white spirit to be precise.