I was only aware that Majora's Mask was made as a collector's edition, and once people found out they had an old, collector's edition, they would sell it for high prices.
But in reality, there was not a grey colored one ever made.
I should know, I own the "collector's edition" and looked it up. A grey one was never made.
For all I know, the collection for gamecube contains most of the NES, N64 games, including Majora's Mask.