The Galaxy S4, Samsung's new flagship phone, appears to have some issues with the display. Earlier there were reports of red subpixels being active when displaying black, but this seems to be solved by the most recent firmware update.
After applying the update, something else is happening. When you're scrolling with a relatively black screen, there's a purple glow before black turns into dark blue. An example of this is when you scroll through the settings. When you move up or down, you can see a purple haze in the dark blue bars and buttons. From the XDA Developers forum it appears that many users suffers from this problem, so it doesn't seem to be incidental.
Update 10:40: The test sample we received at Hardware.Info displays the same issue. It's especially noticeable with rapid scrolling, but the effect isn't extreme, and some people around the office didn't even notice it.
The problems seems to be that the red, green and blue subpixels don't react equally fast when transitioning from black to dark blue. The fact that a purple glow appears, indicates that the red and blue subpixels react faster than the green one. It's unclear whether another firmware update will remedy the problem.
Update: 10:50: We double-checked whether the same things happens on the Galaxy Note II, Note and Galaxy S III, but none of these smartphones exhibit the purple problem of the S4.
Thank you Ritchy IJpelaar for the tip.
This slo-mo video shows how the problem occurs.
The arrows in the image above indicate where the purple problem occurs.
The red glow is clearly visible (older firmware).