Apple's Pro models use aluminum in the current generation, and the color is applied through an anodization process.
Anodization is an electrochemical process that changes the surface of aluminum by creating a controlled oxide layer. That layer can then be colored before being sealed.
The process allows manufacturers to produce durable, visually distinctive finishes without simply painting the exterior like a conventional painted surface.
But anodization is still a surface treatment.
It is not an immutable layer of color embedded throughout the entire piece of aluminum.
That is why factors affecting the oxide layer or its coloration can potentially influence the appearance of the finished product.
MacRumors previously explained that the iPhone 17 Pro's aluminum surface is anodized and that the camera plateau represented a particularly vulnerable area for physical damage. Testing found that most of the shell held up well against everyday objects, while the raised camera area could be more susceptible to scratches because of the construction of its edges.
This does not prove that the iPhone 18 Pro reports have the same cause.
It does, however, explain why the earlier controversy is relevant.
Apple’s Cleaning Guidance Adds Another Layer
Apple's own cleaning instructions provide another piece of the puzzle.
Apple currently advises users that iPhones can be gently cleaned using certain alcohol wipes, including 70 percent isopropyl alcohol wipes and 75 percent ethyl alcohol wipes, as well as Clorox Disinfecting Wipes. At the same time, Apple specifically instructs users not to use products containing bleach or hydrogen peroxide.
Apple also advises users to avoid getting moisture into openings and warns that cleaning products and abrasive materials can damage the phone's finishes or diminish its protective coatings.
The existence of that warning has led some observers to speculate that chemical exposure could be responsible for discoloration.
But it is important not to make a leap that the evidence does not support.
Apple's warning does not say that hydrogen peroxide causes the reported iPhone 18 Pro discoloration.
Nor has Apple publicly stated that peroxide, cleaning chemicals, ultraviolet exposure or another environmental factor is responsible.
The warning is general handling guidance.
Some of the iPhone 17 Pro discoloration reports also came from owners who said they had not used prohibited cleaning products.
One widely discussed owner told MacRumors that they had not used wipes or chemicals on the device and did not believe it had experienced unusual ultraviolet exposure. The phone had reportedly been used with Apple's TechWoven case and occasionally cleaned with a microfiber cloth.
That is one reason the precise cause of the earlier phenomenon remained uncertain.
The same caution should be applied to the iPhone 18 Pro reports.
Burgundy Is Getting Particular Attention
The Burgundy finish has become the most visually prominent part of the latest discussion.
Apple describes Burgundy as one of four official iPhone 18 Pro finishes, alongside Black, Silver and Glacier.
The color is considerably more restrained than the Cosmic Orange finish used on the iPhone 17 Pro, but it is still a saturated color.
That means a subtle change in tone can potentially be easier to see than it would be on a neutral silver surface.
The camera area also occupies a prominent position on the back of the phone.
Any difference between the color of the camera plateau and the surrounding aluminum can therefore become noticeable even when the change itself is relatively small.
Early reports indicate that Silver and Glacier models have not generated the same volume of discoloration complaints. But that observation should not yet be interpreted as evidence that those colors are immune.
The number of reported cases is simply too small to establish reliable differences between finishes.
A much larger sample of devices would be necessary to determine whether one particular color is genuinely more susceptible.
Black Models Have Also Been Mentioned
Black iPhone 18 Pro models have also appeared in reports about apparent changes around the camera area.
That is notable because the Black finish does not have the same visual character as Burgundy.
If similar changes eventually prove to occur across multiple colors, the explanation may be less about the specific pigment and more about the underlying manufacturing or surface-treatment process.
But again, it is too early to draw that conclusion.
A handful of reports cannot establish whether the issue is related to a particular production batch, a specific component, environmental exposure, a finishing process or something else entirely.
It is also possible that more than one phenomenon is being grouped together online.
For example, an actual finish defect, ordinary material transfer, chemical exposure and differences in lighting could all produce photographs that initially appear similar.
That is why controlled examination of affected devices will be more informative than social-media photographs alone.