How do I maintain the rich dark color of lasering stainless steel?

I work for a keyboard manufacture and we are attempting to laser stainless steel keytops with characters. We are getting very good results but we have had people comment that after a short while the dark rich colouring that was left behind after lasering disappears.
In carrying out additional tests we believe that this may be being brought about through the salt content contained in human sweat as simulated tests with a solution of salty water reveals that the characters disappear within 2 hours with type 304 and longer with 316.
We do not understand how the colouring is brought about and are unable to find a solution.
However we do believe that there is an answer as we have carried out the same tests on similar products with fantastic results but we are not in a position to find out how they achieved this.
Are you able to advise?

Try black chrome or nickel, or try some good clearcoat(or combination). Good luck!

Hi Brian
Lasering stainless steel can be done several ways, but if you have the letters etched a dark brown then you are having it done with oxygen a big laser and you are correct.
You need a big laser to etch metal there are lots of plastics that change colour under low power laser and thay are common in keyboards and are indelible as you know.
You will need to get a printing ink into it.
Talk to sericol they do inks for this.
Thanks andy