My friend Àlvaro Serrano, reporting for his site Analog Senses:
"What this means is that, when you sync your pictures to an iOS device using iTunes, your Mac is doing all the heavy lifting behind the scenes, making sure the images are color-matched to the sRGB color space before copying them over to your device.
That’s a clever bit of engineering right there, but what happens if you don’t sync your pictures using a proper authoring tool such as iTunes? What if you simply copy some unmatched JPEG files over to your iPhone by, for example, iMessaging them to yourself or syncing them to a Dropbox folder?
Well, what happens is that iOS’s targeted color management system cannot find the proper relationship between the actual colors in your images and the colors of the sRGB space it knows how to work with, and therefore it can’t display accurate colors."
Álvaro's piece confirmed a phenomenon that I suspected was occurring when looking at different images between my iOS devices and my Mac. It still could be that my MacBook Air's screen is a little off, (I don't think Apple did quite as good a calibration job on these older, non-retina models) but knowing that there is a real reason for the discrepancy in colors is both satisfying in that I'm not going mad, and frustrating in that the discrepancy exists at all.
I can see why nearly a decade ago Apple would have needed to handle color-matching on a Mac, but in a world where my iPad Air 2 is nearly as powerful as one of Apple's brand new machines it just doesn't make a whole lot of logical sense to keep things how they are anymore. Aside from the effort Apple would need to put in to overhaul how iOS handles images and color-matching by default, I don't see any advantage to iOS's current broken method.
I've just given a look to confirm that my camera shoots in sRGB before the images are then transferred over Wi-Fi to one of my iOS devices, and indeed it does. This means that there shouldn't be any issues with my publishing since I'm using an all-mobile, sRGB-only workflow; but this is certainly an issue that affects many users, and Apple ought to issue a fix even if it requires a somewhat substantial overhaul.
After all, it'll only require even more effort to do so as time goes on and iOS continues to develop and change. Better to get it out of the way now.
Cheers, and props to Àlvaro for his digging.