Why it's so hard to find a jet-black iPhone 7

One color of the iPhone 7 and iPhone 7 Plus is really hard to find: jet black.

If you order an iPhone 7 Plus in the shiny, scratchable finish from Apple today, it won't be delivered until November.

There's a lot of reasons for the shortage, but the main one is that Apple is having trouble with jet-black case production, according to a research note from KGI Securities analyst Ming-Chi Kuo obtained by Business Insider.

The jet-black iPhone 7 model "suffers from a low casing production yield rate of 60-70%," writes Kuo. That means that Apple's partners, when producing the new finish, are producing a substantial number of cases that don't meet quality standards.

That's leading to an "undersupply," according to Kuo.

Also contributing to the problem is that "jet-black is the most popular choice," according to a pre-order survey conducted by KGI Securities. Jet-black iPhones accounted for 30-35% of pre-orders worldwide, and nearly half of pre-orders in China, the survey suggests.

"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," Kuo writes.

Ultimately 50% of pre-orderers opted for the iPhone 7 Plus as compared to the smaller model, the survey suggests.

Still, even with the increased demand for jet-black iPhones, Kuo thinks that the iPhone 7 will sell fewer units in 2016 than the iPhone 6S did in 2015.

The initial iPhone 7 shortage was not entirely due to demand, instead, it was constrained by supply. The device launched in 28 countries simultaneously, as compared to 12 last year.

"We maintain our forecast that iPhone 7 shipment volume in 2016 will be lower than that for the iPhone 6S in 2015," Kuo writes.