It sounds quite normal. A friend of mine just got
a young adult in that was being fed Puppy Chow (!).
His coat was all washed out and fuzzy, as you describe.
Just a few weeks of excellent food and his real coat
has come through, darker and the correct texture.
It's simply malnutrition
Same thing happens to
people -- your hair gets brittle and dull. Because hair
grows so quickly the changes can be seen quickly
once you start nourishing the poor baby.