A par-blue bird would have the par-blue mutations on each chromosome...
A par-blue blue bird would have par-blue on one chromosome and blue on the other chromosome.
The "dark blue chromosome" seems to be talking about dark factor... it doesn't have anything to do with par-blue mutations.... or necessarily with the blue mutation at all... perhaps they were just discussing how it could appear.
In example T1, the bird received dark factor and blue mutation from the father. (most likely)
In example T2, the bird received the dark factor from the father, the blue mutation from the mother. (most likely)
Visually speaking, it's the same... a green bird with one dark factor split for blue.
Otherwise, I'm not sure.
