Can't you know that by looking at a swimming pool? Don't think I've seen someone actively refuse to believe this.
[1] https://www.google.com/search?q=what+color+is+water [2] http://crosstalk.cell.com/blog/why-is-the-ocean-different-co...
Looking for misconceptions is a great strategy, thanks!
https://wvbirder.wordpress.com/2016/05/22/bluebirds-and-blue...
(They are blue. Looking blue in white light is the same thing as being blue.)
If one thinks an object is the color it reflects, then add confusion about refraction, and one might easily get to "it looks blue but really isn't".
Science education echos stories, and sometimes those are less than wonderful. Like tabloid journalism narratives, missing the point and leaving readers confused and misled. As with "color from refraction, constructive and destructive interference". IIUC, that interference is mere description of wavelength-dependent differential bending - you still need to absorb the colors you don't wish emerging. But emphasizing "it's not pigment color, it's structural color!", rather than their similarity, can parse as reflection/absorption vs refraction, and conceptually interbreed with real vs apparent object color.
Stories like [1]. The "constructive interference" is "cancelling out" wavelengths, which "is why your eyes perceive" blue. Rather than say, here's one of several mechanisms for pigments to color objects.