This is VERY true. I've used the cold blue solution you can get at Wal Mart or Academy on my father's Ted Williams/Winchester pump gun that he left in a chicken house for a decade. I stripped the barrel as best I could with steel wool. Then I washed it with Dawn in the kitchen sink and put the hair dryer to it. I applied the cold blue with cotton balls and it worked well except for one thing. I had handled the barrel after it was dry with my bare hands. So when the bluing solution went on it permanently sealed my finger prints on the barrel. So I had to do it all over again.
I did an old side by side 16 gauge for a friend in the late 90s with the same solution. It came out very good. I was told that all double barrels are cold blued because if you dunk them in a hot bluing tank it will make two single barrels by dissolving the solder. I have used cold blue on an old SKS just on the spot where I ground off the bayonet mount. It looked good.
On your Marlin it will be tricky like it was on the pump gun I did. By that I mean that the receiver and mag tube were both aluminum and could not be blued. I assume the mag tube on your Marlin is too. On the pump gun I used high heat black engine paint. It wasn't a perfect match but it still looked way better than when I started.
