SOP Blue Swedish:
Drake, bill, greenish blue
Duck, bill, blueish slate 
drake, typically  one or two shades darker than the ducks
Drake, head, dark blue, sometimes approaching black with a green sheen
Duck, head same color as the general body color.
Feathers should be laced with blue and the thickest part of the wing should be very slightly darker blue.
Personal note, I really do not want green heads, so I select for the dark blue head and shy away from the green hues ones, even though the green sheen is allowed in the standard.