Indeed. They would have been of a uniform color...but those old dyes were less high-tech than today's and some would fade-away, leaving the pearls with different colors (because, they all had different colors to start with).
This is what happened to my mom's pearls too.
I also have these dyed freshwater pearls I was given by a customer, they are from the 1980's (she told me this) and they had a mostly uniform color in the late 1990's...but now they've gone to a mostly grayish color with some blue in them, similar to what I'm seeing in your necklace.
The earrings could be from a different source altoghether.