Tahitian Black pearl explained simply
Tahitian Pearls are made from an small nucleus that was inserted into the oyster called "the black lip pearl oyster". Once the operation is completed, The pearl farmer usually wait around 24 month, for the oyster to envelop the nucleus with nacre gradually until it becomes a pearl.
Is Tahitian pearl color naturally black or is it dyed?
Their color are natural, It is the black lip oyster that gives Tahitian Pearls their distinctive hue among other pearls.
Nevertheless, Tahitian Pearls come in a wide range of colors, from graphite hue to metallic silver hue, but the most frequent color is certainly black.
Furthermore, Tahitian Pearls can also have other distinct colors such as green, blue, or purplish hues that makes it very unique.
If you are looking for other natural pearl colors rather than just white, Tahitian pearls might be one of the best options, especially when its about wearing pearl necklace or pearl bracelet that can be different and unique.
Are pearls usually round in shape?
No, Tahitian pearl also come with different shape rather than just round. And each of those shape, (Oval, Teardrop, Circle, Semi-Baroque, Keshi, Baroque) are also well known in the world of jewelry. 
Why other shape are significantly cheaper than a perfect round pearl?
Although farmers assisted the oyster in producing Tahitian pearls: the shape, quality, and even the color of the pearls is decided by nature. Approximatively 5-8%% of the production will be perfectly round pearls and others usually comes in different quality and shapes. Making perfect round pearls extremely valuable.
Does it mean perfect round pearl look way better than others?
Expensive items does not necessarily mean its the best one, other shape might look by far better than a round pearl but still it might be cheaper than a round pearl.
Why Tahitian pearls are cheaper than other pearl?
Depending on the origin of the pearls, some Tahitian pearls may appear to be more affordable than others. When it comes to grading, keep in mind that while there are specific requirements for classifying each pearl, each company may have its own system.
Some companies may be graded as follows:(from highest to lowest quality)
1 - TOP / AAA / AA / A / Bad
2 - A / AB / B / BC / C / CD / D
3 - AAAAA / AAAA / AAA / AA / A
4 - 1 / 1-2 / 2 / 3 / 4
Additionally, the staff sorting the pearls may perceive the quality differently; it is a manual job that requires intuition and is never completely accurate.
Therefore, keep in mind that when comparing each company's pricing, you typically get what you pay for. The lower the price, the more likely you will receive a grade and luster that matches the price.