Description:
Rusty is a mutation in quail that causes them to turn a bright orange color, brighter than Roux (1) and likely brighter than Ginger as well, though a similar dilution. While Roux and Ginger affect the whole feather of the bird and will be a pale red all the way through, the birds with Rusty will have a slate blue undercolor and fluff. (1)
Rusty birds, when tested, were also smaller than pharaoh, Curly, and Rusty+Curly birds from the same breeding program (1). It is unknown if that is just because of the line of birds Rusty was found in or another cause.
It has only been tested once on Pharaoh (1) and it is unknown how common it is outside of a lab setting. It is confirmed to be recessive and not sex-linked, but the locus, gene, and allele that it is on is unknown, as well as how it interacts with any other gene except curly.
Rusty x Rusty = 100% Rusty
Rusty x Plain = 100% Carriers
Rusty x Carrier = 50% Rusty, 50% Carrier
Carrier x Carrier = 25% Rusty, 50% Carrier, 50% Plain
Carrier x Plain = 50% Carrier, 50% Plain
References & Further Reading
Minvielle, F., Gourichon, D., & Moussu, C. (2005). Two new plumage mutations in the Japanese quail:" curly" feather and" rusty" plumage. BMC genetics, 6, 1-5.