I have been in the gem and jewelry business for 35 years and started to buy and use Eithopian opals a few years ago. Some of them turn an orangy color over time. Does anyone know what this is due to? I have not been able to get an answer from any of the vendors I have purchased from.
I also have been collecting and selling Ethiopian Opals for about 3 years + and I do own some orange colored Opals. These Opals were orangy when I purchased them with very nice color.
I have not seen any change color at all. Could it be the way you are storing them, or is something coating them and the coating is turning? I would try to cut one of the opals that are orangy and see what is inside.Take a little off top or bottom and just re-polish when finished.
just a thought hope it helps,