While you can dye leather with coffee, it is not a recommended method as it can be difficult to achieve an even color and the results may not be very long-lasting. If you do decide to try it, make sure to test the coffee on a small hidden area of the leather first to see how it takes to the material. You will also want to use a very weak solution of coffee so that it does not darken the leather too much. Finally, be sure to condition the leather to keep it healthy and hydrated.