I have seen the blue light on BJ7/8 but never on the earlier models. Years ago when I was working on the tach and speedo from my BT7, the small red plastic disk lens fell out of one of the units. I didn't pay attention to which insturment it came from so I can't say if it was for the ignition or high beams.
My recollection is that the blue high beam lights didn't appear on cars until the late sixties or early seventies. Prior to that the high beams were either white or red. At least that is what I recall.
I will say that almost every gold-faced tach and speedo used on the 100-6 thru Mark 2 I have seen on ebay, is missing the colored lens so it's apparent that they weren't installed very securely.