one of the strongest colours i have created so far came from boiling dried hibiscus flowers, sourced locally. the tone is a very cloudy shade of pinky purple, but looks much darker whilst in the dye bath.
in the photo, the small grey bowl in the top right has a sample of bamboo jersey in the dye but the dyebath has had a small trace of bicarbonate of soda added to it, as the chemicals in this are strong enough to alter the final colour. in the case of hibiscus flowers it turns the pink into a more purple tone.
i also found that if the dyebath is left for too long (+3 days) then the liquid will begin to go mouldy because the flowers are still 'alive'