Grammar – Why ‘Consisted Of’ Is Not Grammatical in This Case

It seems that "consisted of" is not grammatical, at least not idiomatic, right?

The above statement is Wrong; "consisted of" is both grammatical and idiomatic. Let's take a look at some examples:

The team consists of four Europeans and two Americans

Would be correct for a team that exists in the present, but if you were talking about a past team, you might say:

The 2014 winning team consisted of four Europeans and two Americans.

If it is something in the past, then using the past tense form of "consist", that is, "consisted", is grammatically correct.

consist of something— phrasal verb with consist verb to be something that is made or formed of various specific things: Cambridge English Dictionary

The crowd consisted mostly of college kids and office workers.

However the statement:

The dispersion of white light into colors by a prism led Sir Isaac Newton to conclude that white light consisted of a mixture of different colors.

...is not technically correct as Sir Issac is referencing all light, it should be consists of. The discovery might have been in the past but the light is still present. (Though it's also worth pointing out that this is exactly the sort of mistake a native speaker might make, especially in casual speech, and people generally wouldn't notice).