Does this look like a rainbow flag to them?
The best way to answer that question is to examine a culture that actually has fewer color words than English -- namely, the Himba people of northern Namibia. They group colors into just five categories: most dark colors (from red to green to purple) are zoozu, white and yellow are vapa, blue is borou (and also some greens, but not those described by zoozu), and dumbu is reds and browns (and also some greens, but not those described by zoozu or borou). Now, watch how this limitation affects their actual perception of color:
Seem like all the same color to you? The Himba man in the clip could, without a moment's hesitation, tell you that the upper-right square is dumbu, while the rest are borou.
How about this one?