Some hybridized versions marketed as Ping Tung revert to a white color at times, and occasionally have a bitter taste. Be certain to acquire your seeds from a reputable source as Chinese companies are marketing these seeds in the US and elsewhere that are not true to their labeling.
Ping Tung as well as all eggplant varieties are highly susceptible to Flea Beetles attack particularly early in the season. Aphids also attack these plants and come later in the season. Varieties of Aphids that attack eggplants are generally either a light blue-green or amber.
Its flavor and color are actually more desirable when harvested before full maturity. When it approaches its full 10 - 12" length the color darkens and it looses a wee bit of its mild taste. Harvesting early will also encourage new growth