The most popular color choice among consumers buying Apple’s brand-new iPhone 7 and Jet Black iPhone 7 Plus is also, apparently, the most difficult for the company to produce, with high failure rates leading to under-supply issues, according to a Wall Street analyst.

While those of us who have ordered the new Apple smartphone models is Matte Black and other color options began getting shipping confirmation numbers and receiving our devices, many customers who have ordered their brand-new smartphone in the Jet Black option have still yet to be charged.

Jet Black iPhone 7 Plus
Image source: Apple

Apple did, in fact, explain that the Jet Black finish requires a lot of work: the smartphone is put through a nine-step anodization and polishing process which gives it that attractive luster, but it is prone to scratching, as Apple suggested that users get themselves a case to prevent it.

While it is well-known that both Matte and Jet Black are popular color choices, it is now known what is to blame for the delay in shipments for the latter color option in both the Jet Black iPhone 7 and the Jet Black iPhone 7 Plus. There is currently a serious shortage in the Jet Black iPhone 7 Plus, and in some cases the estimated shipping dates have been pushed back to November due to manufacturing issues.

According to renowned KGI Securities analyst Ming-Chi Kuo, there are two primary reasons it is incredibly difficult to get one’s hands on a Jet Black iPhone 7.

First, and rather obviously, there is still an incredibly high demand for the Jet Black models, despite its fingerprint- and scratch-prone exterior. This is a standard undersupply problem, according to Kuo. A KGI preorder survey suggests that the Jet Black finish was the most popular, accounting for about a third of all sales worldwide, and almost half of all sales in China.

“The survey offers an insight into iPhone buyers’ tendency to choose models that are aesthetically different from the 6S. Popularity of the Jet Black version indicates that consumers prefer an alternative to the traditional metal finish,” wrote Kuo.

Second, the device is particularly difficult to manufacture without defects. According to Kuo, the phone “suffers from a low casing production yield rate of 60-70 percent,” which correlates to around 30-40 percent of Jet Black iPhones to have some sort of manufacturing defect which prevents the devices from being up to standard for sale.

The combination of these two issues are to be blamed for Apple‘s massive shortage of Jet Black iPhone 7s and iPhone 7 Pluses.

While demand for both the iPhone 7 and iPhone 7 Plus has been high (sales for the devices have already broken record at T-Mobile the time of its preorder launch), Kuo revealed that demand for the device is lower than that of the iPhone 6S when it was released last year.

“Regarding news of some mobile operators reporting preorder growth for the iPhone 7 over last year’s 6S,” explained Kuo, “we believe this is mainly attributable to market share gains for these mobile operators thanks to new promotions, rather than representing greater consumer demand.”

Many wireless carriers and analysts are presenting conflicting data regarding early iPhone sales. Carriers like Sprint and T-Mobile have said that initial demand has never been higher, while analysts are taking a more cautious approach. Unfortunately, this debate cannot be officially settled, as Apple has not yet revealed early iPhone 7 sales data.