[Wheatfield]

Fully extended the Feisol CT3342 tripod is a little tall for me. Would like to mark each tripod leg so they can be extended to the same length. One mark per leg will do. Is there any permanent ink marker that is safe to use on carbon fiber?

Sharpies do just fine, as will nail polish, I expect.
Your local home repair and improvement supplier might stock paint pens in their plumbing department. They will have better visibility because they are pigment, not dye, but there is also the possibility the paint will wear off, probably inside the leg.