A clear and strong apology is necessary. Not one of those "If anyone was offended" deals which suggest the person doesn't really think what they did was that bad. Nah, it needs to be along the lines of "I was wrong. What I did was offensive and I profusely apologize for doing it"

Then, I think the person's evolution from their prior mindset needs to proven through verifiable actions. They can't just SAY they've changed their minds and point to a couple persons of color who are willing to vouch for them. That doesn't carry much weight.

No, there needs to a be a consistent body of work or series of relationships that shows that the person has acted from a more inclusive or empathetic mindset. The less that person immediately has to gain from their "penance", the better.

Without the track record, I tend to think the person has, at best, learned to hide their racism rather than actually overcome it.