I have both a purple and a green, and they are way more different than I thought they'd be.
The purple is a bit looser and warmer, with more crunch tones available. It's definitely got lots of gain but it will only take you up to, say, 1987 in the history of metal. The R1 clean channel is too quiet compared to R2 and lead, it's hard to use. Leads are really ballsy and in-your-face but you can easily dial in too much gain and it sounds harsh. R2 is big, warm, and touch-sensitive. Lead is pretty much useless at lower volumes, R2 doesn't sound good until *real* loud, and even the cleans don't sound very good at low volume.
The green, comparatively, doesn't really have much in the way of "crunch." It's either clean or driving pretty hard. Cleans are very crisp and detailed. High gain tones are really nicely saturated and super tight. It's a player's amp that's best for hard rock and metal. You can really tell that it's the last stop before the MkIV. It's a fair bit louder than the purple, but is a bit better at low volumes.
For me, the purple is more versatile-- I have a gig where I am backing a singer-songwriter with folk-rock and country-rock influences and the green is always either a little too clean or a little too saturated. It has enough usable gain for my sorta-stoner metal gig, but not being able to play real clean and loud is a hassle.
