For yellow dye, plant onions and flowers now and harvest them in spring. Or collect them from other sources (ask for leftover onion skins at grocery stores). Buy wool at knitting shops.
If using onions, you'll need:
1. Wash wool. Soak for 20 minutes in a standard-size plastic dishpan filled halfway with warm water and about 10 drops dishwashing liquid. Gently push wool into water with a spoon, but don't agitate. Rinse in warm water and hang to drain off excess water.
2. Simmer (this step can be done the night before). Fill slow-cooker halfway with cool water. Add onion skins, alum, salt, and vinegar and stir. Add wool and enough additional water to cover. Gently agitate the wool. Simmer for 1 hour. Shut off and let cool.
3. Hang to dry. Wearing gloves, remove wool from slow-cooker and hang to dry on a clothesline (install in an area where dripping dye won't stain anything). Pick off onion skins when dry.
If using flowers: