Most essential oils are photochemically inactive in visible light but do have some reactivity to ultraviolet light.  UV light with high enough energy can cause photochemical reactions in most organic molecules, but is absorbed (not transmitted) by normal glass, regardless of colour. Most of the time it really makes little difference if the oils are in coloured glass. There are a few exceptions, as with the chamazulene-containing oils (blue chamomile, blue yarrow, blue tansy, etc.)The biggest enemies of essential oils are heat and oxygen. Citrus oils and the chamazulene-containing oils are more susceptible to thermal degradation and should be kept in the fridge. Keep all essential oil airspace to a minimum. Once the oil container is half full, then its time to transfer the oil to a smaller bottle. This will significantly extend the useful life of the oil. Keep the airspace to a minimum and the temperature at 75ºF or below (even lower in the case of citrus and other oils more susceptible to thermal decomposition). This way, you can keep the oils smelling nicer for longer periods as well as extend their effectiveness.