The leather has been treated against stains and grease, but aniline leather is susceptible to air and light, because it gets coloured in the pores.
Therefore, you need to protect the leather from stains and grease. You do this by evenly rubbing it with a colourless leather treatment 2 to 3 times a year. You can easily find these products online or in hardware stores.
Please note that the treatment preserves the suppleness of the leather and reduces the absorption of fat, but does not restore colour. As with all 100% leather products, traces of use will develop over time, giving the leather a more worn look. This colour evolution is inherent to aniline leather.