My Bernina 1230 is a wonderful machine, but I'm sure I would get this result if I used the same colors in top and bobbin that you have used. It doesn't matter how much I fine-tune the tension. Some machines seem able to achieve a perfect balance and don't have this problem, but my machine is definitely not one of them.
I'm glad about the other comments, as it never occurred to me that those little dots would disappear when the quilt was washed! That's good to know!
