I agree that the files are not ruined, but that there are better ways to soften the files. Now if you did get them too hot, chunks of steel will be missing...
I assume that is not the case.
To make sure these are as soft as you can get heat them up in another fire and this time make them red hot in day light. Then bury them is warm ashes if possible, cold askes if not. Or warm sand, cold vermiculite if you have any, and etc etc..
Don't try to blue the finished piece as blue will wear off.
When you see a patter steel it is wootze steel or damascus.. You can't really expect to acid etch a patter like on some older shotguns and have it last on a knife.
To get that effect you need another type of steel, and with a file the other type of steel could be a softer mild carbon hot or cold rolled steel.
You would weld these pieces to one another, and heat and fold, heat and fold, heat and fold for so many layers as you please.
2 becomes 4, 4 becomes 16 and etc etc... around 128 layers is about what most people do, but you can fold more yet.. There becomes a point where the folding will sort of loose the effect if a bold pattern is desired.
Another way to color steel is in the tempering, which is done after the hardening, but this too will wear off in use.
To see the effect take a ordinary butter knife and heat the tip with a common propane torch until the tip turns bright blue, and then remove all the heat.
Still remain watching as the heat will run back up the blade.
Once the knive has cooled the tip will be a dull gray, the bright blue will be back up the blade somewhere, and many other colors will be back up the blade more, and end in light gold, or light straw.
The blades you make there after should be some where between dark straw and that blue depending on what type of blade you were making.
A flexible blade for cleaning and fileting a fish might be that blue which is spring steel in effect. A fighter might be dark straw little to no flex, but won't snap like glass. Depending on what else you make it could end up one of the other colors, but the color will wear with use.
I high carbon steel to antique you can use all sorts of things to get a dull gray and or pitted dull gray, but dull gray is about it, maybe shades of black.
Tomatoe paste, vinigar, and clorox bleach are some of the ways.
Get a metal container long enough to hold the blade horizontal, and fill it with oil. I prefer used canolia oil for the high (safer) flash point and the more agreeable smell.
Have a steel lid handy in case you do get a flash. (fire)
Just take one of those soft files and heat it orange hot in day light, get the whole thing at that heat some how. I use a forge or oxy actelen torches.
Test with a magnet. When the steel is hot enough a magnet will hot be attracted, and hold the metal at this heat for a few moments.. You must be sure the suface is heated thru to the other surface.
With big plyiers (tongs) dip the hot file in the quench quickly and move the file easy to get the boiling bubbles off the hot steel.
Instantly pull the file out and allow it to cool. Then clamp it in a vise and with safett glass on, long sleeves, and work gloves, slip a pipe over the file and yank hard. The idea is to see the file break like it was glass.
Then take the bigger part of what ever is left, and what ever is left will be as straight as it was, grind a section bright, but do not get it hot. Use a bucket with water and grind dip, grind dip so you can always touch the steel with your fingers and not be burned.
Now heat the area you made bright watch for the colors you learned on the butter knife, and stop long before you see bright blue, while it may appear still.
Aim for the area to end up all that bright blue however, and once it has quench in the oil..
Now chuck that area in the vise and re-do the pipes test. You should find you can bend the steel and when you let go it comes back to pretty straight, of not straight.
Congrats you just learned a lot more than I knew when I started and ruined just one file of many more ruined files. Really
The good thing is not every file will be ruined after you have 40 hours in it.