Its more a matter of where the cell walls have broken off that affects what symptom you see. Dissolution thins the walls of the anodized cells, eventually eating them away almost completely. If the dissolution is stopped before the cell is completely eaten away, the thin walls will remain, which are easy to fracture and break. On a dyed piece, the closer the break is to the metal substrate, the more of a whitish appearance they take. Since the dye doesn't penetrate the entire depth of the cell, a good portion beneath the dye is still clear. When the cell breaks low, this clear part of the cell shatters and cracks, giving what appears to be a whitish powder. (kind of like salt crystals..salt looks white, until you look at it with a microscope where you see the crystals are clear).
If the cell shatters higher up, there is a higher the percentage of the dye that is present and a lower percentage of the clear cell wall. This will give the powder a color similar to the dye being used.
What appears to have happened in your case is that the tops of the cells, including the sealing plug, have broken off, giving you the colored powder. What remains is a small portion of the clear cell wall, through which you will be able to see the silver of the aluminum metal.
Just a guess without being able to examine the part, but it seems to fit.
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