Green eggplants

[maurodiroma]

Lately my eggplants are more green than the deep purple one is familiar with that vegetable. From what I can tell this color problem doesn't seem to have affected the edible characteristics of the vegetable. Could that be caused by some deficiencies in the soil? The plant is still producing even though the hot summer days are no longer here.

My garden is in southern California.

Any idea?