If its pigmented then a stain remover will work.
I have an aniline in to clean at the moment, which had a load of stains on it, mainly just dirt but also an ink stain.
I used a brush and ultra clean and cleaned it very thoroughly about 3 times. This drastically reduced the staining and also cleaned the leather very well. A wipe over the stain with the alcohol cleaner further reduced it - to the extent of vast improvement. Then to make it belnd in totally, a mist on of colourant to hide the remaining stain.