The reason for the color bleeding is that the producer of the vegetable tanned leather Ecopell uses much less chemicals to preserve the color. You can find detailed information on their website here - https://www.vegetable-tanned-leather.com/. The dye is harmless for the skin and this kind of leather is the best choice for everyone who aims at using the most natural, eco-friendly and allergy-free materials.  The color bleeding is a common issue for slippers or shoes without lining. As written on our site this may happen when there is no leather lining and there is a direct contact of the inner side of the leather and the skin, especially when there is excessive sweating.  Usually these marks can be easily removed and should stop appearing after several times of usage, until the excess leather dye is naturally worn away.