Since the iPhone 4, Apple has taken a leadership role in developing innovative phone cameras. The iPhone 6 and 6 Plus introduce new advances for Apple, including fast "focus-pixel" autofocus and optical image stabilization (in the iPhone 6 Plus). While these features were impressive in our initial tests of both models, and most photos looked pleasing, we often saw fundamental flaws in how the cameras capture colors.

Over several days of testing with an iPhone 6 Plus and two iPhone 6 models, we observed inconsistent white balance that can turn photos slightly purple or magenta, as well as an effect known as chromatic aberration that puts a purple smear on the edge of pictures. We shot identical test photos with iPhone 5 and 5s models, some running iOS 7.1.2 and some running iOS 8.0. The results lead us to suspect that the problems may be software-related, as they were absent or less severe in photos from phones running iOS 7.

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We also took comparison photos with a Galaxy S5 running Android 4.4.2, and didn't see the color problems that cropped up in several of the iPhone images. (We assessed test images on three professional, calibrated LCD monitors and two MacBook Pros with retina displays.) Furthermore, some of the color problems are evident (but not called out) in photos and video from reviews by other tech sites.

We have shared our test photos and videos with Apple, which is investigating the issues we discovered. Because these problems occurred with three iPhone 6 models (plus several more in the other reviews), we are confident that the image-quality glitches are not an isolated fluke. We expect to learn more as Apple continues to analyze the results, but here's what we know so far.

Photos turning pink and purple

Shooting vegetables at a farmers' market in Manhattan's Union Square, we noticed that red peppers appeared purplish in photos from the iPhone 6 and 6 Plus. The effect was far more dramatic when we photographed the hand of one of our testers reaching for an apple from a shaded bin. In the iPhone 6 Plus photo (below left), his hand turns a purplish pink. The same photo taken with a Galaxy S5 (at right) appeared much more natural. These results happened in a shaded but bright farmer's stall — under lighting conditions that photographers call "open shade," which should be ideal for picture taking.

Click the images for larger versions.

iPhone 6 photo at left, Galaxy S5 photo at right

The color problem is likely in the iPhone's white-balance algorithms. As in other cameras, the automatic white-balance function is meant to neutralize any color cast in a scene to make whites look white and everything else appear natural. But the iPhones running iOS 8 were unable to hold a consistent white balance as items in the scene changed. You can see that below in two photos taken with an iPhone 6 Plus. Notice how moving a hand further into the frame changes the overall color.

Two photos taken with the same iPhone 6. Merely changing the position of the hand altered the white balance.

You can see the shift happening in real time in this video below, shot with the same iPhone 6 Plus. The peppers turn from purple to a more natural red when a hand comes into the frame, and hand turns from pink to a natural-looking flesh tone.

In reviewing some of our test photos, Apple representatives said that the colors may have shifted as the result of changing content in different photos. But that's not how white balance works. It takes account of the color of light falling on the subjects, not on the assortment of subjects in a photo. Regardless of what else is happening in the shot, red peppers should never look purple, and white hands shouldn't turn pink.

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Colors shifted like this in many other situations, such as this scene in the park with and without two of us in the foreground. When we stood in front of the camera, the entire scene took on a bluish-green appearance — evident in the exaggerated blue of the shirts and the cyan (light green) tint to the white tents in the background. When we moved out of the frame, the whole scene's coloring shifted to an even bluer shade, as you can see from the color of the pavement. The sky also turns bluer, but that's at least partially the result of the dramatic change in exposure. The iPhone 6 and 6 Plus have face detection, so when we are in the scene, it sets the entire exposure brighter to show our faces brightly.

iPhone 6 Plus photos

We saw similar problems in photos and videos from an iPhone 5 and 5s that were running the new iOS 8 operating system. But we did not see the color issues with an iPhone 5 and 5s running iOS 7, which leads us to believe that Apple may be able to fix the color problem by issuing an update to iOS 8.

The color shifts did not happen in the same photo of us in the park taken with the Galaxy S5, below. The change in exposure is also subtler. This could be because the Galaxy S5 defaults to center-weighted light metering, which optimizes exposure for the center portion of the frame, regardless of what's in it.

Photos taken with Galaxy S5

It's important to note that we didn't see the color problem under all lighting conditions, for example, in this photograph of a co-worker both indoors and outdoors in late afternoon. Her skin appears unnaturally pinkish indoors, while in the outdoor shot, it has a slight warm tone. (The latter is in line with what we've seen from the iPhone 5 and 5s in the past, running iOS 7.) These two photos were taken with an iPhone 6, but we got identical results shooting the pictures simultaneously with an iPhone 5s that was running iOS 8.

iPhone 6 photos indoors and outdoors

Another reviewer's samples

A lot of attention has gone to a review by travel photographer Austin Mann, in cooperation with technology news site The Verge, in which he shot extensively with the iPhone 6, 6 Plus and 5s in Iceland. His photos are attractive, but most have been edited in one or more programs (which he states clearly on his site). Mann and his team also shot an extensive video about the photo trip, using an iPhone 6 and 6 Plus. Mann does not mention editing the video to adjust image quality.

In the film, the magenta (pinkish) cast is stark under low-light conditions, which jibes with our still photo and video findings. Please see the embedded video from Mann's YouTube channel below — especially the skin tones at the following points in the footage: 1:00; 2:52; 3:10; 3:30; and 3:47.

Purple Fringing in iOS 8 Photos

Back to our tests, we also noticed occasional cases of chromatic aberration, in which a harsh contrast between light and dark produces a colored haze — often a purple one. In our experience testing many cameras, a bright light at the edge of the frame, in dark settings, sometimes creates a purple fringe with some cameras and lenses.

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That's exactly what happened in several photos, including in a dark New York subway station with scattered bright lights. It also happened when we photographed the produce section in a gourmet market. A bright light running the length of the shelf above produced varying degrees of purple fringing — from a tad in the upper-left corner to a stripe across the entire top of the picture. In each case, we held the camera in several positions in order to maximize the fringing effect and see how bad it could get. Consequently, the composition of the photos varies a bit.

The iPhone 5 photos fared worse, regardless of whether the cameras were running iOS 7 or 8. The iPhone 5s running iOS 7 never produced a purple fringe, although there was a slight hazy look at the top of the photo. Purple fringing returns with the iPhone 5s running iOS 8, though it's restricted to a small spot in the corner. This suggests that the 5s camera produces less fringe than the iPhone 5 camera, and that iOS 7 helps eliminate the little that does appear. (It's common for modern cameras to clean up flaws like chromatic aberration or lens distortion.) The fact that the purple haze returns in an iPhone 5s with iOS 8 may mean the new operating system is less adept at cleaning up the flaw.

Photos from the iPhone 6 seem to back that up. The purple fringe is equally as small as it is on the iPhone 5s photos. And both cameras are running iOS 8. As with the faulty white balance, it's possible that a software upgrade could also fix the chromatic aberration.

The iPhone 6 has only slight purple frinigng, but it might have none if running iOS 7.

We saw no chromatic aberration in any of several dozen Galaxy S5 photos shot in the same settings as the iPhone photos that do show it. (Composition is slightly different due to the camera's wider aspect ratio, but again, our main goal was to maximize the chance of chromatic aberration.)

The Galaxy S5 never exhibited purple fringing in any of the comparison photos we shot.

It may be that Android 4.2 is better at removing the artifact, or that the design of the camera prevents it. The iPhone 5 and 5s cameras are flush with the back of the phone, while the iPhone 6 and 6 Plus cameras protrude slightly. The Galaxy S5 camera, in comparison, is slightly recessed. This might block light from hitting the lens from the side, which is often a cause of chromatic aberration.

We still can't say definitively what is causing these image-quality problems. Nor do we know if the problems can be fixed. We expect to know more as Apple continues to investigate, and we'll keep you in the loop.

Contact senior editor Sean Captain at scaptain@tomsguide.com if you are having an iPhone 6 problems, or for any other scoops. And follow me @seancaptain and on flicker at Sergiocapitano. Senior photographer Jeremy Lips and senior editor Mike Prospero contributed extensively to this article. Follow us @tomsguide, on Facebook and on Google+.