CMYK, RGB or sRGB?
When publishing to tablets, often I get asked what color model to use. And especially as many publishers or corporates want to reuse Print articles and pictures, they ask whether it is ok to use CMYK, as converting would add additional time.
As always the question isn’t really easy to answer, as it depends on the system or solution you have and of course also on the device you expect your customers and readers to use. And even if you know what tablet all your readers will have, e.g. as you are creating an in-house app using Apple’s Enterprise program and you only distribute iPads with Retina Display (aka iPad4), it is tough to answer, as the ambiance light and brightness setting of the devices also influence perceived color.
So let’s assume you are publishing to iOS devices only. Apple changed the color performance of their devices significantly over generations. The iPhone for example uses a limited sRGB space whereas the colorspace of the iPhone 5 is almost identical to sRGB. The iPad mini however has again a limited sRGB space again, so even smaller than sRGB.
On Android devices it is similar, though newer devices like the Nexus 7 and the Kindle Fire HD again have a colorspace almost identical to sRGB.
So my general advice can only be: Use sRGB (not RGB!) as your target colorspace and test!
Automated or manual conversion?
That’s a tough one to answer. It really depends whether you are using a software or solution to publish digitally or whether you do it by hand. As far as I know, currently no tablet or smartphone uses ICC profiles to calibrate its screen so far, when you use alternative browsers like mobile Firefox it can be possible (but, will the majority of your readers use that? Probably not).
So if you publish manually (meaning, you are not using a solution), I’d recommend to convert manually (e.g. batch converting all pictures) to sRGB.
If you are using a Digital Publishing software solution, such as App Studio, then you should be fine using CMYK as App Studio automatically uses an sRGB output profile. However it’s probably a good idea to simulate sRGB on screen (using the Color Management function of InDesign or QuarkXPress) to see the close to final results.
Still, do proof-check on at least a few devices to see whether color looks as expected, as laptop screens and computer monitors typically have a wider colorspace (RGB) than tablets (sRGB).
If you want to read more details about the screens of mobile devices, then I can recommend dot-color.com, which I found really helpful:
Do tablets show accurate color?
Color performance of the iPhone 5: