In Thailand, people actually only use white pepper, but black pepper is a fine substitute. White pepper is a little stronger and cleaner in flavor and I prefer it for most dishes, such as Pad Thai and Gang Leang. While many western dishes are much better with fresh ground pepper, most Thai dishes are better with pre-ground pepper.
Here in the US, ground white pepper from Thailand comes in a small tin box that looks like it came out of the 1920's.
Pepper is a vine that grows on a stake and has tentacles similar to orchid roots. The peppercorn bunch is 3- 5 inches long with small round green berries. When ripened, the peppercorn turns from green to yellow and red.
Black pepper is harvested while the peppercorn is ripe, but still green and is then sun dried. Green peppercorn yeilds 33% black pepper by weight.
White peppercorn requires much more work. The peppercorn is picked when the it is red and fully ripened. The peppercorn is soaked in water to soften the husk for 5-7 days. The husk is then removed. The peppercorn is then sun dried. Ripe peppercorns yield 27 percent white pepper by weight. Since white pepper does not have the husk, it is stronger than black pepper.
If you can find the white pepper kernels at oriental grocery stores, you will find that they are frequently much less expensive than major American brands (like 1/3 the cost). Black pepper is also frequently much less expensive.