Okay, let me quote myself and bold the parts to aid those who apparently have a hard time reading plain English.
Ace Flibble said:
Stainless frets definitely change the tone. Having recently switched a guitar from standard to stainless frets, I can safely say the guitar now retains a lot more higher frequencies. Like the difference between a Tele bridge pickup with and without a metal baseplate, or new vs worn strings.
And to those who somehow (head injury, perhaps?) doubt this, try the following: buy a metal pickguard. Not a metal-looking pickguard, one actually made of metal. Steel would be most relevant, obviously. Don't change anything else about the guitar—even save the same strings, if you can—but do switch the pickguards. You'll notice that even with guitar designs like Les Paul Junriors, where the pickguard does not contact the strings, bridge, controls, jack or pickups, the tone still gets very noticably brighter. Not just a little bit, but a whole lot. For those who don't think a pickguard is enough of an example, try using a guitar with a metal nut, or try switching bridge saddles from brass or zinc to steel or titanium.
There is not a single person who would debate that changing to a steel nut or saddles is going to change the tone, so why on Earth would you ever think that changing the frets would be any different? They are in contact with the strings as much as either other part.
And like I said, and now restated, I very recently changed a guitar from nickel-silver to stainless steel frets—nothign else about the guitar was changed—and the tone jumped up in brightness so much I thought I had accidentally disconnected the volume and tone controls. The owner of the guitar noticed it too and I've now got the guitar in again to change the saddles and pickups to try to curb the brightness back down.
But apparently our ears believe in myths.