Egg color (shades of brown) and the E gene...

[NatJ]

Of course, none of the above sheds any light on egg color

There's some information in F.B. Hutt's book, The Genetics of the Fowl.
It was published back in 1949, and someone republished it more recently, but buying a copy in print costs a lot more than I think any book should

Ooh, I just found it online here
https://digital.library.cornell.edu/catalog/chla2837819
Egg color information starts on the book page numbered 380 (can't remember what page of the digital format it was.)