[GreenKeys] different teletype ribbon colors

[Jim Haynes]

I would say "probably" not, because military installations often used
multiple copy paper.

Purple ribbon was popular in some places; I know W.U. used it and also
the wire services from time to time.  Maybe the purple ink is particularly
penetrating.

I know in Europe it was popular to use red/black ribbon where red was
for whatever was typed on the local keyboard and black was what was
received over the wire.  But I don't know how red/black was used in the
U.S.