There is data on the anime that continues to circulate years after the end of a series, and this is one of the fandom favorites. On The Quintessential Quintuplets (d)Gotoubun no Hanayome), each sister Nakano She has a different hair color on screen, but canonically, within the story, that never existed.
The quintuplets of The Quintessential Quintuplets Do you have the same hair color?

Yes. According to the canon of the series, the five sisters Nakano They are physically identical to each other, including the color of your hair. The different shades that we see on the screen, Ichika’s pink, Nino’s blue, Miku green, Yotsuba’s purple and Itsuki orange, were a purely visual production decision, designed so that the public could distinguish each sister easily at first glance.
Within the narrative universe of the story, however, the quintuplets share a completely identical physique, with no difference in hair color that distinguishes them from each other.
Why did Futarou have so much difficulty recognizing them?

This revelation directly explains one of the most commented, and sometimes criticized, narrative elements of the series: the constant difficulty of the protagonist, Futarou Uesugi, to distinguish each of the sisters at the beginning of the story.
For a good part of the audience, this confusion seemed exaggerated or forced as a narrative resource, especially since from the viewer’s perspective the visual differences are evident thanks to the colors of hair. But if within the story the five sisters are truly indistinguishable on a physical level, Futarou’s difficulty in recognizing them ceases to be an exaggeration and becomes a logical and coherent consequence of the real canon of the series.
This distinction is key to understanding one of the central tensions of the plot: Futarou’s challenge was not simply to memorize colors, but to genuinely learn to know the personality, gestures and way of speaking of each sister in order to differentiate them, something much more aligned with the central theme. of the story about the individual identity versus the shared appearance.
Why does this data continue to generate conversation in the fandom?

The striking thing about this curiosity is that it is not a new fact within the franchise The Quintessential Quintuplets, but it continues to resurface periodically on social networks and fan communities, generating the same surprise reaction every time. Part of his comical effect comes from something very specific: for years, a good part of the fandom debated and “took” for his favorite quintilla, based, in part, on his hair color as a distinctive feature of personality or aesthetics, a trait that, technically, never It existed within the real canon of history.
This generated a wave of jokes within the community, where many fans point out with humor that they spent years defending their favorite character based on a visual characteristic that was, from the beginning, a tool of production and not a canonical element of the narrative world.
a more common visual resource than it seems

This type of design decision, assigning distinctive colors to characters that in the original story are visually identical or very similar, is a relatively common practice in the anime, especially in series that present groups of characters with a shared base design. The function is purely practical: helping the audience to visually process who is who without relying exclusively on the narrative context or dialogue.
in the event of Gotoubun no Hanayome, this decision turned out to be particularly effective from the commercial and marketing point of view, since the distinctive colors of each sister became a fundamental part of the visual identity of the franchise, present in all its merchandising, promotional art and marketing material, even if, within the world of history, those colors never really existed.