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This is not a simple question because a lot of factors are involved; type of ink, type of leather, type of leather dye, delay of intervention, intervention with other products...
In short, there is no guaranties of success when it comes to ink but here are some tips:
URAD: URAD does remove ink stains on "Corrected and Pigmented Grain" and "Full Grained Pigmented", most of the time. The trick is to use as little as possible. Just dip 1/8 of an inch of one corner of the sponge into the jar, and wipe it off the side of the jar. Now rub vigorously quickly on the ink spot.... The sponge is just a bit more abrasive that way than if you would use too much, yet there's just enough product to help dissolve the ink...
"Full Grain Aniline" has no protection at all, the ink just goes right in. For that kind of leather, I believe you will need to rub hard, almost scrub it off with one drop of URAD on one tip of the sponge. It's the scrubbing that will do most of the work so YES, there is always a risk the color will not come back completely.

AQUILA: Our leather shampoo called AQUILA can clean fresh ink stains but usually does not do better than URAD. It was made to clean body grease, not ink.

If you do not have the above products at hand, you can try a "Q-tip" with some "Isopropyl Alcohol". (Local pharmacy) Apply with the Q-tip only to the ink spot, at first, do not let sit to long. Wipe with a wet (but not too wet) cloth. If it comes off, repeat. If it does not come off, let the alcohol stand a bit longer. If that does not do it. Use nail polish remover in the same fashion.
P.S. The nail polish remover...can be a delicate operation since it can also take out the leather's dye. Use with caution.
P.S. Prevention tips: spray Sahara stainproofing when new. Then have a jar of URAD handy, just in case someone has the urge to draw a smiley face on your new $5000 sofa!
I think that prevention is worth the money!

If Urad, rubbing alcohol and nail polish remover did not remove the stain, we know if nothing that will.
Costa-Brava(dye):When cleaning does not work, you could try to hide it using URAD with color, which is not a dye but could cover the stain a bit. If you apply Urad with color, use 1 to 2 Tbls of Urad (let's say BLACK) mixed in 5oz of TENDERLY, then apply.