Amish clothing is dark-colored. Not from gloom — from logic.
Reasons
Practicality: dark fabric hides dirt. A farmer works in soil, manure, machine oil. A white shirt goes gray in a day. Navy — looks clean for a week.
Equality: if everyone wears the same colors — no 'rich' and 'poor' colors. Red silk vs brown cotton = inequality. All in navy = equal.
Modesty: bright colors attract attention. An Amish person shouldn't stand out — Gelassenheit.
Durability: dark dyes (indigo, walnut, oak bark) are the most durable natural dyes. Bright ones (berries, flowers) fade in a few washes.
Exceptions
Children's clothes — lighter and brighter colors allowed (blue, pink, green). Before baptism a child isn't bound by Ordnung. Wedding dress — blue (not white! White = vanity). Kapp — white (married). Shirts — can be light blue (work).
Fact
Black isn't everyday color. Black is for church, funerals, formal occasions. Everyday — navy, brown, burgundy, green.