Similar to Blue Tansy and German Chamomile, some essential oils from yarrow can contain chamazulene which gives the oil a dark blue colour. Some yarrow essential oils are dark blue and contain over 15% chamazulene, which can act as a great natural colourant for your skincare formulation.
During the steam distillation of the herb, a compound called matricine is converted to azulene or chamazulene, compounds which are not present in the actual plant. It is only through the application of heat and the process of steam distillation that azulene and chamazulene develop.