Yes I have tried several different dyes several times. For the first few months afterwards the seats looked brand new...but slowly they'll start to fade again so that six months later, they'll be just as faded as they were when you started.

I never messed with the cheap spray dyes that you can buy in the stores. I got my dyes from paint dealers or upholsterers.

Btw, if you every ask a upholsterer, you'll probably get the same answer.