You asked: Is the destruction/absorbing of the black (indigo) people still in progress? If so, why does the UB state that amalgamation of the races is not necessary for a planet to attain light and life, only oneness of religion and language?
And you also asked: Would black people (indigo) exist today if this were a normal, regular world? The UB describes them as secondary, inferior, and backward. Would they have been destroyed with the green and orange races?
You two questions are basically asking the same kind of thing: whether the Indigo race is doomed to obliteration on normal worlds, and on the kind of world that we have, which is decidedly not normal.
One thing, though...here are a few passage that you may have been referring to above.
55:3.1 During this age of light and life the world increasingly prospers under the fatherly rule of the Planetary Sovereign. By this time the worlds are progressing under the momentum of one language, one religion, and, on normal spheres, one race.
55:3.21 The great handicap confronting Urantia in the matter of attaining the high planetary destiny of light and life is embraced in the problems of disease, degeneracy, war, multicolored races, and multilingualism.
55:3.22 No evolutionary world can hope to progress beyond the first stage of settledness in light until it has achieved one language, one religion, and one philosophy. Being of one race greatly facilitates such achievement, but the many peoples of Urantia do not preclude the attainment of higher stages.
I am not sure where you read that "amalgamation of the races is not necessary for a planet to attain light and life, only oneness of religion and language." Normal planets develop towards the blending of the races under the watchcare of Adam and Eve; we lost our Adam and Eve. So, maybe you read this passage as saying that we will enjoy some leeway in getting to the early stages of light and life. In any event, I do think that the final stages of light and life will see Urantia on a one-race course, difficult as it may be to achieve without the presence of Adam and Eve.
As for the Indigo peoples being singled out for obliteration – I don't think this is the case. On a normal world, the final color of mankind is a olive hue – a mixing of all the races. At that time, none of the original six colored races will have survived as such. All peoples will be the same color, upstepped by the violet life plasm.
52:3.7 By the end of the Adamic dispensation on a normal planet the races are practically blended, so that it can be truly proclaimed that "God has made of one blood all the nations," and that his Son "has made of one color all peoples." The color of such an amalgamated race is somewhat of an olive shade of the violet hue, the racial "white" of the spheres.
The green and orange races are extinct, as you have pointed out. Even on our disordered world, all of the races were meant to be blended, producing a superior race that contains the best from all the races. That some of them become "extinct" is a function of the normal course of evolution – the stronger overcoming the weaker, all the while preserving what was good about the old, creating a superior development that combines the best of all. And this does not mean that the entire race is obliterated; some of the individuals of the race survive, those remaining strains being absorbed into the others.
80:1.4 But during earlier times there was little to hinder the westward migration of the Adamites. The Sahara was an open grazing land overspread by herders and agriculturists. These Saharans never engaged in manufacture, nor were they city builders. They were an indigo-black group which carried extensive strains of the extinct green and orange races. But they received a very limited amount of the violet inheritance before the upthrust of land and the shifting water-laden winds dispersed the remnants of this prosperous and peaceful civilization.
52:1.3 Primitive men are mighty hunters and fierce fighters. The law of this age is the physical survival of the fittest; the government of these times is wholly tribal. During the early racial struggles on many worlds some of the evolutionary races are obliterated, as occurred on Urantia. Those who survive are usually subsequently blended with the later imported violet race, the Adamic peoples.
It would appear that eventually, all pure line individuals of these six races would be blended into the mix, so maybe one could say that they are eliminated (not deliberately destroyed) in that way; not necessarily because of their not being fit, but because the best of the race has been incorporated, and the remnants die out.
On our planet, very little is normal, as you know. No matter what, strains of the Indigo race are irrevocably blended in, as are all other races. The real finessing should have taken place when Adam and Eve lived here in the Garden, but since the default, we've been on a different course altogether.
Now, this next passage is saying that since Adam and Eve are no longer here, there is no one competent to judge whether one race is better than another. And, each major ethnicity is mixed anyway...not mixed as Adam and Eve's plan might have done it, but nonetheless...
51:4.8 These six evolutionary races are destined to be blended and exalted by amalgamation with the progeny of the Adamic uplifters. But before these peoples are blended, the inferior and unfit are largely eliminated. The Planetary Prince and the Material Son, with other suitable planetary authorities, pass upon the fitness of the reproducing strains. The difficulty of executing such a radical program on Urantia consists in the absence of competent judges to pass upon the biologic fitness or unfitness of the individuals of your world races. Notwithstanding this obstacle, it seems that you ought to be able to agree upon the biologic disfellowshiping of your more markedly unfit, defective, degenerate, and antisocial stocks.
As you can see, it is only the "inferior and unfit" that are deliberately eliminated through the Adamic regimes; and this refers to only reproducing individuals – not entire races of people. It would appear that all of the races have this possibility of producing unfit or degenerate stocks. It is the purpose of the Adamic bestowal to correct all of these issues. It wasn't done.
As it is, ALL of the races on Urantia are blended now; no pure line strains of any of the races remain. Due to the effects of the irregularities of our Adamic default, race amalgamation did not go according to plan. Even the appearance of the six races on Urantia was irregular, so nothing has really gone according to plan here as far as the racial mixing is concerned.
Click to read more: The Six Evolutionary Races
Thanks again for this thoughtful question. I hope that my answer has been helpful.