The new, darker design of YouTube is currently being released. These alterations result in a more significant upgrade than was anticipated. YouTube for Android is currently testing a video progress bar that is not always red.
When you are passively watching a video on one of our Android devices with the dark theme enabled, the progress bar on YouTube is white/gray rather than the usual red. YouTube also fails to indicate how much of a video has been loaded in those circumstances.
The scrubber returns to its previous state, complete with loading status, upon interaction or tapping to bring up controls. This assists the UI with disappearing, which is something that YouTube has been pursuing as seen with Encompassing mode.
Red is still used in the main feed and everywhere else outside of the video player, so the change aims to improve the viewing experience. As YouTube’s inflection tone, red is most certainly not disappearing.
When using a light theme on the same device, the usual red progress bar remains. It is unclear whether that is the intended behavior of red on white being less distracting or merely a component of the A/B test.
This change is not widely implemented and only works on that one phone, even when signed in with multiple devices.