The Amish wear plain clothing in specific colors. Many of these can be made from plants.
Mordant
Before dyeing, fabric is soaked in mordant — a solution that fixes dye. Alum is the safest: 10g per liter water, soak fabric 1 hour.
Colors
Yellow: onion skins (30 min boil). Brown: walnut shells (boil 1 hour). Blue: indigo (ferment 1 week). Pink: beet (not durable without mordant). Green: first yellow (onion), then blue (indigo). Grey/black: oak bark + rusty nail in water (iron-tannin reaction).
Process
Soak dye material overnight. Boil 1 hour. Strain. Submerge mordanted fabric. Hold at 80°C for 1–2 hours. Don't boil — color will be dull. Remove, rinse in cold water.
Durability
With proper mordant, natural dyes withstand dozens of washes. Color is softer and deeper than synthetic — ages beautifully, doesn't fade in blotches.