What is the purpose of the blue folder icon in Windows?

I've always been surprised by the number of icons that Windows has in shell32.dll and imageres.dll. I noticed that there is a blue folder (shown) and that I had never seen it before under Windows.

Blue folders

With my research, I found only questions about the folder compression icon (the arrows – thank you, Google). I am absolutely sure that there is a significant use for them.

Has any one ever used them? I only used them manually to bring out some files. Does Microsoft have something to say for them?