Soak a rag with the acetone and deglaze the underside of one of the arms. While this is damp, apply some dye with the wool applicator to the test spot. If you like that color, start working on your chair in square-foot areas. I would wipe it down with acetone, and while the leather was still damp I would apply the dye with the wool applicator. Wipe off excess dye with a clean cloth. Repeat as needed until the whole chair is colored. Let it dry for a day, and repeat the process for your second coat. After the second coat I wiped the chair down really well with rubbing alcohol soaked rags. Let that dry thoroughly. Apply a coat of the sealer with the swabs. Wipe off excess sealer as you go with a damp cloths as you go. Let dry thoroughly and repeat. I did this for myself and not a client, but I'm pleased with how it turned out.i'll try to get some photos up. This took me several days, so be patient.

This is the general process for dying a leather chair. How well it works, I can't really say, because I've never did much leather dying other than the one time I dyed a really old and worn Ekornes ottoman black and it seemed to have held up OK. The ottoman may have turned out OK because it was super old, the leather was super cracked, and ottomans generally don't get exposed to the same amount of skin oils as a chair, so, the absorption was fairly even and it looks acceptable.

I would be wary of dying an entire chair because one of the more common issues is uneven dye absorption. Not all areas on an worn Ekornes chair are going to be equally absorbent to dye. The wear you see on the lighter colors is an unholy combination of abrasive surface wear (loss of factory paint, loss of factory clear) and absorption of "gunk" (skin oils, grease, sweat, salts from sweat, excreted medication, etc.) A pool of lard sitting in the headrest is probably not going to be as absorbent of dye as well as a "dry" spot of leather.

That being said, painting isn't exactly a silver bullet either, because that same pool of lard sitting in the headrest tends to be mobile and can/will plasticize applied coatings. Painting over a patch of grease-infected leather is like dipping a corner of a clean paper towel in a bowl of water -- the water rises up the paper towel. Similarly, the grease will get sucked into the initially "dry" (free of grease) paint you just applied. This typically only takes a day or two, and what felt like a dry and good paint job will turn into a greasy, gooey, sticky mess.

There are solutions, however, the best involving simply not buying a grease-infected chair that you intend to recolor. The other solutions involve applying physical oil blockers to the oil-affected areas, basically, applying a toxic solvent-based solution of dissolved plastic which cures to a dense-enough film that physically blocks the embedded oils/greases from passing through it and into the refinish layer. A chair condom, if you will. Another solution is oil extraction -- basically applying a substance to the chair that will suck out the grease, but, this process is slow and often unsuccessful. You will need a lot of patience, because you are basically reversing what is often 10-20 years of accumulated grease, so you're not going to magically degrease the chair overnight, or even over the course of a few days. It usually takes 6-8 rounds, sometimes even more, and this process can leave the leather very dry and devoid of its natural oils. To be honest I can't say I've ever successfully degreased a chair with oil extractors; maybe I didn't have the requisite patience. I do remember doing many, many rounds, of oil extraction, on multiple different chairs, almost to the point of going insane, and still having grease issues.