Julius Caesar was assassinated for wearing red boots. Barrack Obama was lambasted for wearing a tan suit. Purple is associated with royalty, white is associated with clergy, and gold is associated with superiority. Red and Blue have powerful meanings in America, and so does Green. Which colour is the most political in your opinion?
Black has the most universal meaning of solidarity, seriousness, mourning, and formality across cultures and peoples.
Japanese budhist monks use black for their clothes as it simbolizes purity, or as black being the most pure color. In very few instances, they may wear purple or gold, but that’s due status and a latter addition.
In a funeral, only the deceased would wear white, I don’t remember why though, but for a while wearing white was in bad taste.
Wearing all black is also common for the Catholic clergy, and for a long time most brides used black for their wedding dress: https://kentuckykindredgenealogy.com/2014/12/13/history-of-the-black-wedding-dress/