Dark brown polish will take them to a tan color and black polish will take them to a dark tan or mid-brown color. It takes guts (an maybe a smidge of insanity
to do this but it is quite possible. I've done several pairs successfully. You are not going to get a nice even color this way - they will come out with an antique look. I like that look myself. You may want to pick up an old pair of shoes at a thrift store first so you can practice. And if you don't want to do it yourself a good shoe repair shop should be able to help you.