':' was the traditional directory separator on Macintosh systems before OSX, therefore it can't be used on HFS+ either. I remember there being some FS funk when OSX came out since it was very common for people to put dates in their filenames using slashes, and well, UNIX doesn't like that. I don't know what APFS does.

As I understand it, : and / get swapped depending on whether you use unix APIs (/ is a directory separator, : is plain) or mac APIs (: is a directory separator and / is plain)

From what I recall (had a macbook years ago) I could put colons in filenames in the terminal, but not in finder.

NTFS can't have colons in filenames because they are used to name alternate data streams.

https://docs.microsoft.com/en-us/sysinternals/downloads/stre...

Also HDFS. This bit me the first time I tried to write a Hadoop job that wrote every run to a new output dir.