My impression is that "home value" is often a dodge that sounds better on paper than "I don't like change". You generally can't sue over hurt feelings, but if you can attach some kind of monetary value to it then the courts may take your case.
As you note home value is an extremely nebulous concept as it is tied to whatever people who currently do not live in the community might pay to buy a house. No matter what someone sells for they can always say "it would have sold for more if every single house was painted exactly the same shade of beige, you miscreants with your off white, ecru, and oatmeal houses have cost me tens of thousands of dollars!"
As you note home value is an extremely nebulous concept as it is tied to whatever people who currently do not live in the community might pay to buy a house. No matter what someone sells for they can always say "it would have sold for more if every single house was painted exactly the same shade of beige, you miscreants with your off white, ecru, and oatmeal houses have cost me tens of thousands of dollars!"