Apple

No one knows, but no rumors have surfaced so far about it. I don't know what Apple can do, honestly. The main way it senses that it's on a wrist, reads heart rate, reads blood oxygen, and so on is with light refraction. Ink can cause the light sensors to not read properly. Light-based sensors seem to be the industry standard, and the only good option for non-invasive reading. Ink is going to interfere with the light.