I think I know, but I just don't know.

[PotterWatch]

Did you actually see that egg come out? Those look exactly like brown leghorn hens which should lay white eggs.

 

[speckledhen]

Welsummers and Brown Leghorns look similar at first glance, but Leghorns lay white and Welsummers lay brown. Are you sure that egg came from that hen? It would be really weird to have a brown Leghorn lay a brown egg, but Welsummers have red earlobes, not white.

 

[CarriageStone]

I swear I saw one of these girls hopping up from a small brown egg. Perhaps I was mistaken.

 

[PotterWatch]

They could have been sitting in the nest where one of the others had laid an egg. Unless you saw a brown egg being laid by one of those girls, I would say they lay white ones.