Evidence indicates it originally came from the middle east.
Even today, many breeds from that area show evidence of it in their phenotype. However, because indigo has varying expression depending up the base color, it wasn t described as something genetically different until the mid-thirties. Wendell Levi and Willard F. Hollander, in unison, worked out the genetics of indigo. I m not going to go into the now sixty year old history, but if you re interested this effort is describe in Levi s book, The Pigeon . Suffice it to say, though, that indigo was found to be non-sex linked dominant in its inheritance.