Is it true that good pistachio nuts should have yellowish shell, purplish skin and greenish flesh?
The natural colors for pistacio meats are green, yellow-green, purple and/or red.  Shells are beige.  The Kerman variety, which account for 90% of the pistachios grown in California, are yellow-green to deep green.  Pistacios from Iran tend to be more in the red-purple spectrum, and are alleged by their partisans to be superior to California pistacios.  Personally, I like both the Kerman and the Iranian ones I've been able to sample.

Looking at the picture, I'd say that those nuts were clearly bleached, due to the excessive whiteness of the shells.  This seems to be a common practice in China, enough to cause the government to debate a ban on bleaching. Per that article and others, there is no health risk associated with peroxide bleaching, but there is thought to be a significant loss of vitamins due to bleaching.