A device can have different "states". The color located next to the device name, provides you with a quick overview as to the status The color at the edge of the field with the device (group) name gives a quick overview of the status of a device.
SCREENSHOT Any changes made to the playlist or settings are synchronized with the device. The device has reported back in a timely manner to the defined update interval and, if necessary made any updates or changes. 
 SCREENSHOT If the device has a yellow bar, then changes have been made (configuration, playlist or device group) which have not yet been synchronized with the player. Yellow means, so to speak: wait until the next update interval synchronizes the data and brings the device up to date.
SCREENSHOT A red bar indicates that the device has not synchronized during the specified update interval. Important: a red bar does not mean that content will no longer be played. It means that content which is being displayed is not the most up to date. For example, it might be that the contents of the assigned playlist do not match the contents of the playlist in the viewneo account, since there have been changes since the last synchronization.