It almost goes without saying (though we do say it a lot) that a developer preview is not necessarily an accurate picture of the final product. We're reminded of that today when it comes to the second Android M developer preview. The dark system UI mode that debuted in the first preview is gone in this one, but it's not time to panic yet.

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Left: first preview, Right: second preview

There was much celebration when the dark UI mode was spotted in the developer settings a few weeks ago. It swapped the blindingly bright material light settings UI for a material dark one. There was even an automatic setting that would switch to dark mode at night and back to light in the morning. It seemed to work fine, but it's missing in the new preview. It should be right above the "Debugging" heading.

From what we've heard, the dark UI mode might not have been completely ready for use last time. The fact that it's gone now could mean its inclusion last time was simply an oversight. This doesn't mean that the dark UI won't be in the final version of Android M, but we can't say for sure right now.