Moscow Blue Deltas have got two major traits.
the blue Moscow Metal Head and an additional Trait, which makes in addition with this Moscow Metal Head a whole blue fish. For itself this trait colors the peduncle and often also the caudalfin blueish dark.
Cause it is the traits , which makes in addition with the metalhead the Moscow Blue, wie call it M(moscow)B(lue)A(dditional)G(ene) (or in german MoskauBlauErgänzungsGen= MBEG).
In Modern Moscow Blues both traits can be on Y or/and on X....this depend on the strain.
Traditional it was Moscow Metalhead = Y and MBAG = X.
these DS I have showing clearly the Moscow Head and the dark peduncle+swords and also some grey/white markings at the fins...maybe from another fincolor-trait( maybe additional an DS trait).
here you can see one male in teasing action with the typical moscow blue shining in head-region.