TLDR: Ethiopian opals are also found in more abundance than Australian ones, making them more readily available at a lower price. It is unfortunate, but inevitable, they will eventually turn yellow after a short time. 

Not all opals are created equal, but they are all beautiful! The two most widely debated are Ethiopian and Australian opals.

Ethiopian Opals – Formed amongst volcanic rock in the Wollo province of Ethiopia, these opals are very hydrophanous. Prone to absorbing most staining liquids, you will want to avoid direct contact with skin oils, perfumes, quick changes of humidity in the air, and more.

Once absorbed, most opals become discolored and unstable.

Care tips for beaded Ethiopian opals:

• Wear over clothing to help prevent any of your natural skin oils from being absorbed.
• Do not touch them unless your hands are clean. Wash off any hand lotions, hand sanitizer, sunscreen, or if you have touched any household cleansers. To be safe, always wash your hands before touching the opals.
• Remember the rule of wearing pearls: last on, first off. If you plan on wearing your opals, put them on right before you leave, and take them off first thing when you get home. Of course, wash your hands before taking them off.
• Do not wear them while getting ready. Makeup, perfume, and hairspray all play a factor in discoloring Ethiopian opals. 
• When putting them away, first wipe them with a clean microfiber cloth. This will help remove any dirt, debris, and oils. 
• Store them inside a Ziploc bag with some cotton, especially in high humidity. But you don't want them stored away too long because they can then become too dry and crack. So every few days, take them out to let them breathe. Ethiopian opals carry a high percentage of water. 

Australian Opals are priced much higher and ever-increasing. Recently two of the most primary source mines of Australian opals closed, making sourcing these incredible gems hard and costlier. They also are not hydrophanous, and will never change color.

Ethiopian opals are also found in more abundance than Australian ones, making them more readily available at a lower price. It is unfortunate, but inevitable, they will eventually turn yellow after a short time.