It'd be nice if the distinction between the previous and upcoming pattern were more, well, distinct. I know that the pattern is greyed out, but I still find myself trying to go past the end accidentally. If there were, say, a 2px thick line between the current pattern and those on either side, it'd make life a bit easier.
Does your request for changeable mask color probably be enough of a workaround to close this one? If the difference between the current and prev/next patterns is not visible enough, you can just make it more obvious in the next version making the prev/next patterns darker.
Oo-err... Kinda, I guess. :) I'm actually using the "next version" already. :P
Thing is, though, if we could put some kind of visual indication between patterns, and have them flow completely seamlessly into each other (without even a mask), then we would basically be bridging the gap between sequencing and tracking -- the pattern editor would essentially become one long piece of paper.
You could also do some nice things here, like have a slightly different effect for +++-divided patterns, and so on.
I'd really rather you *didn't* close this one, then, because I do think that it has merit, and that there are some use cases that it would really work for.