Lifted from the Yahoo Harrison site:
"As I was unable to get anyone here (or on uk.rec.models.engineering) to
come up with a BS/RAL number for the M300 colours, I contacted the
Harrison customer support team. To my pleasant surprise, I got a very
prompt and helpful response from the sales team (to whom it was passed).
After clarification of the serial number*, the lathe was dated to 1977,
and the answer was (quote):
"The paint references at this time were RAL 26049/Q55/9 for the grey and
BS337/Q55/6 for the olive brown type colour"."
I assume the olive brown colour is what is used on the M series, and the grey on the earlier models.