On the Ezana Stone, who are the black and red people that the Ethiopian king was referring to?

Ezana is a Semetic or Semetized king, who came in power by defeated the Kush/Ethiopians (including Nubians), Nilotics and even the Semites (Aksumites, Habashits and Sabeans). He and his Aksumite tribe ruled the kingdom.

During Ezana's march to clear the commercial routes for accessing trade destinations, the areas were inhabited by Baza people under the Bazin Kingdom from 100 - 360 BCE. unfortunately there is a misreading of the name Haza (it should have been Baza). So the references made to Haza and Barya people is in actual reading refers to "Baza and Barya". These people today are known or referred to as Baza (Kunama) and Barya (Nara).

There is no clear explanation how the name Kunama came to be attributed to Baza. Until the late 1800s the name Kunama was not in the books of history as a tribal name for the Baza. In fact, to date these people are known as Baza in the Sudan and some parts of western Eritrea. Ezana's reference to blacks could only refer to the Baza and Nara people and the "Red" people refers to the marching people from the Mediterranean and Persia who were coming to these areas to seek trading items such as ivory, incense, gold etc.

Back in the 1970s I read in an edition of Family of Man magazine that the "Black Noba" refers to the Nuba peoples of the Nuba Mountains in the southern part of what is now the Republic of Sudan (close to the border with South Sudan), whereas the "Red Noba" refers to the Nubians of northern Sudan and southern Egypt. Confusion can arise today because in Sudan the term "Nuba" is applied to both groups.

While I'm not 100% sure, I would guess the red and black are meant to distinguish between the 2 groups currently in Sudan, who are both called Nuba. In North Sudan and Southern Egypt, the Nuba have a lighter black skin complexion, similar to other Northeast African communities (Tigray, Somali, Beja), while the Nuba of the South are Nilotic and more closely related to the Dinka for instance.

Claude Riley, one of the most important historians to discuss Kush and the Nile Valley history, also mentions that there was a North-South division in Kush, with separate ethnic groups living in the region.

The reason why it is debatable is because many people assume Kush was a h*m*geneous area with a single ethnic group, which wouldn't make sense since it was huge.

So my idea is the 'Red' are the ancestors of the modern day North Sudanese inhabitants (the Riverine Nubians and the Arabised groups), while the 'black' are the ancestors of the Hill Nuba and other groups closely related to them(Dinka, Nuer, Daju etc.)

The people Ezana is referencing are the red Noba who are of the Napata kingdom and the Nara & Kunama tribe of Eritrea are the blacks.

Red is a phrase used in east Africa for light skin, not necessarily red. Both these tribes races are Cush descendants.

We don’t really know for sure who the Noba were, and as far as I can tell Ezana is the only source to distinguish Red and Black Noba. A footnote in this article cites an interpretation that the Black Noba were from the south while Red Noba were from the north. You may want to check the original source on that. A different article has another relevant footnote which states that “Ezana classified a number of his own subjects and those along his border as ‘red’ or ‘black’”, citing certain pages in a book by Pankhurst.

(Disclaimer: I have zero expertise on the history of East Africa.)

The short answer is that we really don't know with any certainty, and there is - as yet - no scholarly consensus on the subject.

The names given to ancient peoples (in this case from the early fourth century CE) often have little meaning in modern contexts. However, it does seem reasonable to associate the names 'Kasu' with Kushites and 'Nuba' with Nubians in this instance.

In this case, the state of research was summarised by Stuart Munro-Hay in his book Aksum: an African Civilisation of Late Antiquity (Edinburgh University Press, 1991), which - I suspect - was probably also the original source for the excepts from the text of the DAE 11 inscription you quote in the question.

He says:

We know from Ezana's 'monotheist' inscription (Ch. 11: 5 [‘The Aksumite Inscriptions’]) that the Aksumites recognised the Black (tsalim) and the Red (qayh) peoples, mentioning also the 'Red Noba'; but it is not clear where in these categories they fitted themselves. Littmann [Deutsche Aksum-Expedition] (1913) thought that the implication was of the 'red' people of the kingdom of Aksum in contrast to the 'black' Noba (and others), a differentiation which still applies today in the eyes of the northern Ethiopians. Both Drewes [Inscriptions de l'Éthiopie antique] (1962: 98) and Schneider [Les inscriptions d'Enda Čerqos] (1961: 61-2), whose particular study has been the pre-Aksumite inscriptions, have come to the conclusion that even in the time of the kingdom of D'MT this contrast was used. The expression 'the entire kingdom' was rendered in the geographical sense by the phrase `its east and its west', while the different characteristics of its population were illustrated by the words 'its red (people) and its black (people)'. If this is correct, and the two phrases are intentionally balanced, it might indicate a predominance of the 'red' or semiticised population in the eastern and central part of the kingdom, as would be expected given the South Arabian influences apparent from the material remains found there.

I have added links to the texts cited by Hay.

From this, we can see that it is by no means clear even whether the Aksumites considered themselves among the 'black' ('tsalim') or the 'red' ('qayh') peoples, let alone what that distinction meant when they applied it to the Nuba.

Given the above, it doesn't appear that we can really say anything meaningful about the peoples of Egypt to the north on the basis of this text. I certainly don't see what it can contribute to the 'long standing controversy around the original phenotype of those who founded the Nile valley civilization'.