Which country are you thinking of?

Statistics of course can't work if there is no deviation, but I can't think of a country which is ethnically homogeneous.

Countries with a high degree of homogeneity, like South Korea and Japan, still have their own forms of racism. For example, https://en.wikipedia.org/wiki/Racism_in_South_Korea says many students "have difficulties maintaining relationships with students who do not share the same nationality background ... because of their classmates' different skin colors".

> which is ethnically homogeneous

Like Poland after world war two?

Was post-war Poland more homogeneous than current-day Japan or South Korea? https://en.wikipedia.org/wiki/Demographic_history_of_Poland doesn't tell me numbers, saying only of that era:

> Ukrainians resp. Rusyns, the largest minority group, are scattered in various northern districts. Lesser numbers of Belarusians and Lithuanians live in areas adjoining Belarus and Lithuania. The Jewish community, almost entirely Polonized, has been greatly reduced. In Silesia a significant segment of the population, of mixed Polish and German ancestry, tends to declare itself as Polish or German according to political circumstances. Minorities of Germans remain in Pomerania, Silesia, East Prussia, and Lubus.

> Small populations of Polish Tatars still exist.

That's not 100% ethnically homogeneous, which means in principle there could have been ethnic discrimination.

I guess so, looking at South Africa or other African countries where ethnicities with Western features historically got preferential treatment.

There are no such countries AFAIK. Societies seem to find ways to divide into “tribes” one way or another.