1. Amber/Brown: Amber or brown dropper bottles are popular as they are known to protect essential oils from harmful UV rays, which can degrade the oils over time. These bottles are also considered the best option for storing and transporting essential oils due to their ability to prevent breakage.

2. Blue: Blue dropper bottles are excellent for storing oils that require protection from light but do not necessarily need the protection offered by amber or brown bottles. The blue color provides a good balance of protection while still allowing product visibility.

3. Clear: Clear dropper bottles are the most popular option due to their transparency, allowing easy identification of the oil inside. However, they should only be used for oils that do not need protection from UV rays.

4. Green: Green dropper bottles are ideal for oils that are sensitive to light and require maximum protection. They also tend to be thicker and more durable than other types of bottles.

5. Purple: Purple dropper bottles are not as common but are still a great option for storing essential oils that require protection from UV rays. The color provides a more elegant and unique look.

Overall, the color of the plastic essential oil dropper bottles is important as it can affect the quality and longevity of the oils. Choosing the right color based on the specific needs of the oil can help preserve its potency and fragrance for a longer period of time.