This bird looks like a few things going on...
The melanistic coloring (black) around the head...
http://users.skynet.be/fa398872/engoulm03.htm
the dirty white breast of the breast.. Also called blue bar by some lacks any black/mealanistic modifications anywhere on the body. This only affects the breast area,without any black.
http://users.skynet.be/fa398872/engoulm27.htm
It is hard to tell sometimes what is going on. Most times the bird will regain the normal colors once diet and sunlight are improved. The main cause of melanistic coloring.
Sometimes the melanistic colors are in the first set of feathers and once the bird molts the next year, the color return to normal.
Sometimes however, even with great diet and plenty of natural sunlight and with subsequent molts the bird retains the blue coloring. This may be the start of a new mutation and not simply a modification due to enviromental conditions..... only time will tell
Very interesting oddball, though I would recommend ensuring this bird gets a varied diet, including complete minerals and some sunshine
