Most Spanish are caucasian, as are most people in the North shore of the Mediterranean.
If the ancients were taking humans off the Earth 300,000 or so years ago, which version of archaic humans were they taking? All of the following were around in that time period:
Homo neanderthalensis, Homo rhodesiensis, or possibly Homo erectus?
They weren't taking Homo sapiens (i.e. modern humans) because they weren't around at that point. We didn't show up until around 200,000 years ago.
Last theories I've read suggest Homo Neanderthalensis and Homo Sapiens were interfertile, and the Homo Neandertalensis was in most part absorbed into the current Homo by intermarriage, instead of disapearing.
In any case, if the Ancients took Human (or proto human) samples about 300000 years ago, it's quite easy to believe they have evoluted into other ethnic groups (even without Ancient intervention) just because the environmental factors were different tan in Earth.
If in Earth, with more close environmental conditions we have divided in the many etnic groups we have today, I cannot imagine how could me ndiffer if they evolutioned in different planets, under different suns (with different light wavelengths), etc...
Most of the ethnic breakouts for Earth I have run across give this:
Asian (Including Indian Subcontinent) 60.6%, Black 14.1%, White 16.7%, Latino 8.5%
I won't discuss those numbers, of course, but that does not mean all moved to stars keeping in them. Traveller was written in the late 1970's, when most space exploration (and so the ones seen as more likely to move to stars) were Western World or Russian, while the Asians (60% of population, as you say) were below them in space tech.
Also, the fact that the language envolved from the Solomani taling the Vilani empire is Galanglic, so evoluted (mainly) from English, not from Mandarin (as would be logical if the Chinese led the move, as numbers would suggest). That makes me think most of this taking (and so the move to stars) was by Western (mostly caucasian) people.
And even so, I guess most Imperial people will be more evolutioned from Vilani tan from Solomani, as the Vilani had already a quite more large population base, having been in the stars for about 2000 years when the Terrans began its move.
As an example, remember that the Sword Worlds (one of the major expeditions/colonizaions that went farther) are told to be mainly from the Nordic/Germanic etnic group (caucasian)...
EDIT: I'd say more a Western bias and product of its time (about 35 years ago) that racism