All the rapid color control might be out of the reach of the current hardware, OTOH have you seen where it's explicitly stated by Apple to being restricted to the "s" models? The "s" are running iOS 9 implicitly, so there's a possibility it's a software feature....
Apple's own literature is all about a "custom display chip".
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Apple's own literature is all about a "custom display chip".
http://www.apple.com/iphone-6s/cameras/