When IR light is allowed to pass through to the sensor, the IR light contaminates the channels (mostly the red channel) with information that was not visible in the original scene. The result is an image with a color cast. […] The iPhone 4 image shows a reddish cast due to the extra IR light recorded on the red channel. The 4S image shows a background which much more closely resembles the original scene.
More accurate colors are captured by the iPhone 4S. As for displaying those colors the Retina Display on the iPhone 4 is a better choice.