Mujjo answer:

“I am sorry to hear that you are disappointed with the way your slate green case turned out. We use full-grain leather, a type of leather that is very natural and develops its own character while you’re using it. The leather absorbs the oils and lotions from your hands; which varies from person to person, making each case unique to the user.

When these oils are absorbed, the leather develops a deeper and darker color but also attracts dirt more easily. As you can see, with your case, the patina is most visible at the points where there has been the most wear and tear, such as putting in a pocket. Moreover, the lighter the color of the leather, the more obvious the patina that it acquires.

I hope I answered your question clearly. If you have a new full-grain leather product in the future, a leather protection spray might help to slow down the patina process.”