Q:

New Stack Exchange top bar shows green achievements popup

I like the new Stack Exchange top bar, but I have have noticed sometimes the Achievements popup icon is shown in green.
I am not talking about this one: 
Sometimes it shows this icon green:

like this:

Is it some type of feature or bug of Stack Exchange?
Note: I have notice it in Firefox and Safari.

A:

It's a feature. 
When you get an achievement that doesn't award reputation (for example, when you get a badge), the icon lights up green.

