Thats a hard question, and depends very much on the material conditions in a place. In countries where indigenous people are a majority, it would definitely mean giving state control to the indigenous. But in countries like the US where colonizers are the majority, I cant imagine how it could be solved in a good way. You cant really send white people away after they lived there for generations, but you also cant allow them to have majority control over the state.

Surely there must be some writing about this somewhere, maybe from the Black Panthers or other groups in the US?

In my opinion, I believe it would be best to give them a territory in which they are allowed to govern themselves, and pick up where they left off. Adopt a hands off policy, and let their group culture develop in a way that is most conducive to what strengths as a race and the territory allotted, if the goal of your program was to try and place disadvantaged minorities on equal footing, it would begin with unplugging them from the dysfunctional culture that has been IV-Dripped into them for generations.

Once a culture emphasizing functionality and progress is developed, it may be possible to begin relations between sovereign nations/territories, not as a user and use-ee, but as neighbors, or even allies.

Obviously reparations are moral, considering the hoffic crimes of imperialism. I guess the issue is that reparations in capitalism will mean monetary transfer from one capitalist entity to another one. I am not sure if any justice will be achieved without fundamentally overcoming capitalism. A real socialist society will focus on the most marginalized and transition to a society where real equality would exist, which ideally achieve what reparations would seek to do.

Simple.

Genocide of the Oppressors.