The Bible similarly compares Jews with Canaanites, Moabites, Philistines, Arameans, and Mesopotamians. None of those comparisons have anything to do with physical appearance, any more than the comparison with the Ethiopians do. A look at such quotes in context makes it clear that the comparisons have to do either with the (mis)behavior of the Jewish People or with God's reminder that He values all peoples, and has done great things for others as well as for the Jews.
And while I would wish to see the quote from Tacitus in full context and in the original to be certain, I will also venture to say that he has been found wrong in many places. There is no reason to suppose this any other than one of those instances.
I'm sorry, but there is simply no basis in history for these statements. There just isn't a shred of evidence to support such claims, any scholar of the Ancient Near East can tell you that.
Also,
cham (חם
in Hebrew has nothing to do with blackness, it simply means "hot," and probably was originally a nickname referring to temperament. The word for black in Hebrew is
shachor (שחור
. The two words don't even share a common root, let alone meaning.
Also, Jerusalem fell and the Temple was destroyed in 70 CE, not 66.
And the Romans and Israelites probably had roughly similar coloring. The Romans might have been a bit lighter toned in complexion, but were definitely darker than most northern Italians-- and many southern Italians-- today, that much seems clear from the historical accounts of them.
It is true that most European Jews have limited Semitic ancestry, but the notion that the majority of European Jews were Khazars is a false one. The one Jewish anthropologist who professed the idea has since retracted his claims, and no reputable science has emerged to uphold such an idea. Furthermore, there have been several studies that show that many Jews, from many worldwide communities, share certain genetic markers. Of especial note is the Kohen gene, a mitochondrial gene marker shared by over 90% of kohanim (priests) no matter which Jewish community they come from-- European, Middle Eastern, African, Asian, whatever. Today, the notion that most European Jews are descended from Khazar converts is usually used by anti-Semites in attempts to delegitimize the Jewish People. The idea should be shunned as false.
They weren't. They would have been about the same shade as modern Iraqis. Who are, by and large, not black.