Clean your avocado stones and skins thoroughly and place them in a large saucepan. Add enough water so that it will cover the fabric when you add it (but don't add it yet).
Bring the pot to a low boil, then reduce the heat and simmer very gently for at least 30 minutes.
Once you're happy with the colour, remove the stones or pits and strain the dye through a muslin or cheesecloth to remove all of the residue.
Add your fabric to the dye pot. Keep the fabric on a very low heat to keep it warm, or turn it off, as you prefer.
Leave the fabric in the dye pot for a full day and night, or until it reaches your desired shade, stirring every now and again so you get an even colour.
The next day, take your fabric out and rinse it with a gentle detergent. Hang to dry.