That's an amazing looking Jack. The blue gene Jack Dempsey or BGJD for short, is the result of breeding a Electric Blue Jack Dempsey (EBJD) with a normal Jack Dempsey. All their offspring will look the same as a normal Jack but carry the blue gene. If you then breed the BGJD again with an EBJD, you receive a percentage of EBJD. I'm not 100% positive on the percentages but I did read them somewhere.
EBJD x JD = 100% BGJD
EBJD x BGJD = 50% EBJD|25% BGJD|25% JD (you can't tell which are blue genes and which are normal)
BGJD x BGJD = 25% EBJD|25% BGJD|50% JD (you can't tell which are blue genes and which are normal)
Those should be the numbers if I remember correctly... Only way to know for sure is if you breed him with a BGJD female.
EBJD x JD = 100% BGJD
EBJD x BGJD = 50% EBJD|50% BGJD
BGJD x BGJD = 25% EBJD|25% BGJD|50% JD (you can't tell which are blue genes and which are normal)
EBJD x JD = 100% BGJD
EBJD x BGJD = 50% EBJD|50% BGJD
BGJD x BGJD = 25% EBJD|25% BGJD|50% JD (you can't tell which are blue genes and which are normal)