Based on the date (1989) and the fact that it is simul-class, I would have to guess it is a green stripe. Could also be blue stripe. I recommend to check with Mesa Boogie, as they should be able to tell you for sure.
(The difference between blue stripe and green stripe is the triode vs. pentode wiring. I am pretty sure there is a thread on the Boogie board that will tell you how to distinguish this by looking at the wiring of the tube sockets....)
Good luck!