I remember a thread on this topic some time ago, but it seems to have vanished. I need my memory refreshed on when the blue hands changed to the familiar black ones, then for a time post WWII went back to blue and finally in later 1940s went back to black and remained black through the end of production.

If it's the thread I recall, it was:

C001 to C30000 (approximately on all) - blued hands, bright steel center on the minute hand.

C30000 to C120000 - black

C12000 to C200000 - blue, no steel center minute hand.

C200000 and above - black.

Thanks much! Exactly the information I was looking for.