John Greenall, the "Turnout Guru" of the carriage driving world, says that if you want to darken your brown leather gloves, just rub them on a sweaty horse.
Also, Krissy is right that shoes/boots and belts should match. Actually, they should match the color of the harness, so if you have black harness, you should have black footwear and belt (if you wear one). This goes even if the rest of your turnout is brown, i.e. brown coat/blouse. Russet harness should have brown footwear. It used to be that the metal on the vehicle also had to match the harness, but they have loosened up on that b/c it is a challenge to completely repaint your vehicle just because you have russet harness, but the leather on the vehicle should be russet, too. Russet harness should only be used with a natural (not painted) wood vehicle.
I knew of a competitor that had a russet harness and a natural wood vehicle with brown painted metal. She also had carriage lamps with brown metal, and she was told by Mr. Greenall that carriage lamps were never painted brown, and therefore, should still remain black even though the rest of the vehicle was brown. Yes, carriage driving is steeped in tradition and "good taste". Even your (subtle) jewelry and buttons should match, no mixing silver and gold. (Does not apply to bits and buckle tongues where strength is needed.)
