Old Question Posed Again To PDMLers

[Bob Blakely]

It's been some time since I asked this question (perhaps four or so years). 
We now have new members and also you older members have gained knowledge (or 
resources for knowledge), so I again pose this question:

I have a lens, K85/1.8, where the last three digits of the serial number 
are, from the factory, in red.

Why?
Regards,
Bob...