Blue streaks/stripes?!?

[RobinB]

One of my Shadow Boxing plants is now producing fruits with blue zig zag streaks or stripes. It didn't start out this way. Early in the season, the fruit were red with green stripes with just a dusting of blue on the shoulders. Then the blue started "creeping down" the tomatoes as the season progressed. Now, like other blue tomatoes I've grown and seen, the red color is pure only at the tip. I don't have a lot of experience with blue tomatoes, but is this kind of a progression withing a season normal? All I know is that now, in the last week or so, I have some blue stripes. I swear, a couple of weeks ago, the stripes were GREEN.

Oh yeah, they taste AMAZING!