I found this with a 3 second google search…..
https://www.healthline.com/health/code-blue

@flo You are incorrect. Code blue is an emergency situation where all available hospital personnel go to the patients room to perhaps save a life. Friends and loved ones are not to run to the room and get in the way of doctors and nurses.
This is pretty much on any TV doctor show.
@SQUEEKY2 One more to add to your list that we have at our hospital is “code walker”. It means that an elderly person is missing.

In schools (at least the ones I know) it’s code red for fire and code black for intruders/threats to the school. In this case it’s important to know what to do in those situations. For red, as is the case in more first situations, everyone evacuates to a pre-determined open area, usually the school oval. In terms of code black, everyone goes inside to the nearest classroom with a teacher (it’s likely that if it’s going to occur it will be during classes), the doors are locked, lights turned off, blinds drawn until a second announcement comes over the speaker to announce it’s safe to leave.

I’m in Australia, the only time I’ve ever been through a code black was when someone spilt something suspicious near school; although I understand it would be different in other countries

Some retailers use codes for suspected theft, or if someone needs security right away. It varies by retailer I think. I doubt there is a standard for that like in hospitals.

We have color codes for certain types of bad weather.
I almost don’t notice it any longer, when they get announced, because the weather hardly ever delivers….

In the clinic where my wife worked they would call a “Dr. Fleet” for a fainting incident. She worked in the lab and they usually had at least one person pass out every week having their blood drawn for testing.

50+ years ago Modell’s Shoppers World had 2 codes: WM and WB.
WM meant: clean up needed – with mop
WB meant: clean up needed – with broom

@SQUEEKY2 Thanks but I was asking anywhere not just in hospitals.
@chyna I think most people (98% or something ) are too sensible to go in and get in the way. And a patiient can still be only alive for a very short time after the personnel work on him/her, which is why I brought up “in case it’s the last time.”

So, because of the small percentage the public who would go in and get in the way, the visitors should not know what code blue is about?

When my fellow teachers want to meet for drinks after work, we pass the word that there is a safety committee meeting at 3:30. This was confusing at first, as I chaired the actual safety committee.

@LuckyGuy What if some people think Code Blue is cleaning related?