The second revision was the "Purple Stripe" Mark III, which featured a purple marker stripe above the power cord. This amplifier was identical in component values and R2 channel as the later Black Stripes, but had a lead section much closer to a IIC+ https://en.wikipedia.org/wiki/Mesa_Boogie_Mark_Series
The blacks & purples are more like a C / C+ in terms of gain. They're a lot less aggressive than the more hairy reds, blues & greens.
IIs and IIIs are a lot more raw & organic than the later Marks. The IIs have better clarity, though. Splitting hairs of course, on stage you'd be hard pressed to tell the difference between any of them.
The 60W amps are the most pissed off. The Simuls are smoother being that the Class A pair is wired Triode.
well the main thing i remember from owning two of these, is that there is a little purple line in sharpie above the power cord.
it had the power to magically reduce the resale value slightly.
on a serious note. it has a different board than the blue, red, and green stripes. i found it to be the least "pissed off" of all the stripes, if that makes sense.