www.allthingsdempsey.com
is another good dempsey site to read through for Blue Dempsey information...
A Blue x Blue pair can spawn and will produce 100% blue fry... but to date the only person I know of that says to have kept any alive says they were all deformed.
If you want a beautiful pair of fish and do not care about producing offspring... then a Blue x Blue pair is perfect for you...
If you wish to breed them I highly suggest reading as much as possible about them so you can make the most informed decisions as possible along the way. This color morph has experienced a lot of inbreeding and has several genetic weaknesses that need to be logically corrected in the breeding process.
In my opinion and my opinion alone, if your not going to do something to strengthen the line, then leave breeding to those who are... but by all means enjoy the fish!
Best of luck whichever direction you go with!