Are you kidding me? You are arguing that unless a scientific paper claims that hops add color, you will refuse to believe that yellow resin and green vegetal matter will change anything at all to water's color? Even when faced with actual pictures of it? Do you need one to prove that water is wet? That the earth isn't the center of the universe? I don't think that claiming that making a solution between colorful ingredients and water will result in something that doesn't look like pure water requires a peer-reviewed publication.
Sorry, but there aren't scientific papers on every possible subject. It needs to be worth a scientist's time, and have some sort of utility. Why would anyone write a scientific article on the impacts of hops on water? Hops are used for *beer*, not water. Wort is quite different, because wort has color.
"I'm skeptical that hops would add significant color." Define significant? Because nobody's claiming that a small amount of hops will add a huge amount of color or turbidity. Blaming the guy's hop tea color on oxidation? Have you ever even handled hops? Just handling them colors one's hands. Not sure how you could blame oxidation when picking them right from the plant enough to paint your fingers, can't really get any more fresh than that.
/Can/ you filter/treat everything out of a brew to remove color? Sure, pass it through reverse osmosis, charcoal filters, etc., if you want, but then that doesn't negate the fact that hop matter has color to begin with, it's just that your later operations reduced its impacts. Time/filtering/precipitation can remove a lot of turbidity and color, in some cases, but I'm not aware of any case where it will turn a solution completely transparent (without adding chemicals strong enough to turn your brew into poison, anyways).
If you don't want to believe it, then don't. Your book cites three factors that add color. If you want to take this as gospel and believe that since this guy only states 3 things, only 3 things could ever add color, then that's on you. I doubt even the author believes that. Those are certainly the 3 *main* things that add color to *beer*, but it doesn't negate the contributions of hops on water or near-water solutions.
I assume the alcohol content in beer doesn't extract any more colors as hops are added during boil of wort when no alcohol is present.
Nilo, there is alcohol present in the solution when/if dry hopping. And assuming the point of the hop additions is to add flavor/aroma to an otherwise really bland dilute must, dry hopping is probably going to be used. Ethanol is a much better solvent for organic compounds like oils and resins than water is.