"Right on"

[Jonathon Green]

It's certainly in the 1968 edition of _Current Slang_ III:2, subtitled
'The Slang of Watts'. I think Jesse might be being a trifle restrictive; I
definitely recall being very well aware of the term in mid-late 1969,
certainly in the context of working on the London 'underground press',
albeit at that stage for the short-lived UK edition of a still relatively
radical Rolling Stone. In other words, we were far, both lit. and fig.,
 from the Black Panthers.  We probably picked it up through the old UPS
(the Underground Press Syndicate, via which all such papers circulated
material).

Jonathon Green