Quote: Yes, white paired to non-white is unpredictable. Every white can give different results as white prevents expression of the other colour and pattern genes they have.
All chickens have either gold or silver (boys can have one gene of each). Melanizers or their lack can prevent or allow leakage of ground colour.
My educated guess is still a guess. Start marking which pen your eggs are from, and that will allow you to narrow down the culprits. An e^b black tends to have a less than pure glossy black colouring, but unless placed alongside a glossy black, it may not be noticeable. e^b is very recessive, so it can hide, too.