This is evidence inconsistent with the hypothesis, which weakens by undermining the argument's phenomenon-hypothesis structure. If the number of color words in a language truly corresponded to speakers' ability to distinguish those colors, we would expect English-speakers to be less able to distinguish shades of blue, compared to Russian-speakers who have distinct words for those shades. (A) tells us that this prediction of the hypothesis is untrue, which undermines the argument.

(A) weakens the argument even though the argument discusses languages with fewer color words than English, because this is the exact same type of relationship between languages. The author's hypothesis is based on a general principle that speakers of languages with fewer color words can distinguish fewer colors. Even though the author applies that principle to English specifically, undermining the principle also undermines the application.

If (B) does anything, it just sets a lower bound on the number of color words in a typical language: at least two, for red and everything else. That doesn't help us with the relationship between numbers of color words and color distinction, which is what the author's hypothesis is actually about.

(C) tells us that Khmer and English define the boundaries between color words differently, but we don't know if they have different numbers of color words—or if Khmer-speakers and English-speakers actually perceive different numbers of colors. (C) doesn't help us evaluate the hypothesis because it doesn't give us enough relevant information.

(C) really focuses on qualitative differences in colors—which objects are judged to match which color words? The issue is, the argument is just about numbers. The author only cares about the number of color words and the number of colors people can distinguish. (C) doesn't give us any information about these numbers.

Like (B), (D) describes a similarity between languages, but one that is not relevant to the argument. The argument isn't affected by the origins of words, and (D) doesn't give us any way to relate word origin to the numbers of color words (or the number of colors perceived) that the author is concerned with.

(E) gives us a difference in color words—we know English has a word for gray, and now we know that most other languages don't. However, (E) doesn't relate this difference to color perception, so it isn't able to weaken the argument. Sure, gray is commonly found in nature, but can non-English-speakers distinguish gray from other colors? We still don't know, which prevents us from weakening.

If we had some reason to believe that all people can distinguish all colors commonly found in nature, then (E) would weaken the argument. In that case, it would concretely tell us that speakers of many languages could distinguish a color even without a word for that color. But without that missing piece, (E) doesn't get us all the way to our goal.