As a passenger I noticed set of five indicators on ceiling at the front of the 737 passenger cabin. They are: red, yellow (or white), blue, white, red.
Red ones seem to be coupled together (what could indicate their higher importance and also prevents problem with failed light bulb).
On the photo, there seem to be two white indicators but on older models I almost certainly remember that one of them was yellow.
I have seen those indicators in old and new 737 models. I understand they inform the cabin crew of something but I did not find explanation so far.
What is the exact purpose of each indicator?
Are they controlled manually or automatically?
Are they Boeing-specific?
How are similar conditions communicated to cabin crew in other similar types of aircrafts (e.g. A320) which do not seem to have these indicators?