Jeg tror det er fordi når de laver parfumen så følger farven fra de ting der er i med.. men er ikke sikker.. kunne bare godt tyde på det... :)
Der er jo forskellige måder at lave dem på.. her er 2..:
Expression: Raw material is squeezed or compressed and the oils are collected. Of all raw materials, only the fragrant oils from the peels of fruits in the citrus family are extracted in this manner since the oil is present in large enough quantities as to make this extraction method economically feasible.
Distillation: A common technique for obtaining aromatic compounds from plants, such as orange blossoms and roses. The raw material is heated and the fragrant compounds are re-collected through condensation of the distilled vapour.
Du kan finde resten på dette link: ---->>
http://en.wikipedia.org/wiki/Perfume <--- bare led efter overskriften "Obtaining Natural Odorants"
håber det hjælper dig :)