The most probable way it was produced is to cross a Blue with a Gold... in which will produce all normal looking offspring that are Het for both Blue and Gold... or "Blue Gene" as well as "Gold Gene"...
Then these double het offspring are raised and bred together... yielding a wild mix of offspring with 6.25% likely being both Blue and Gold...
I would expect all the offspring from a Blue/Gold x Blue/Gold would die just like they do with Blue x Blue crossing...
But if we were to cross a Blue/Gold x Het Blue / Het Gold (or Blue Gene/Gold Gene) then we could expect 25% Blue/Gold (25% Blue Het Gold, 25% Gold Het Blue & 25% Double Hets).