I had the same problem on some black borders I did. No amount of playing with tension could ever get it right for me, but I just couldn't face using the same color thread front and back.
Promise not to laugh and I'll tell you what I did to "fix it." Promise?........
I got the tension issues to the best point I could, but the little with dots still showed on the front but the black quit showing on the back. I quilted it to the best of my limited abilities and then.....................got out my fine tipped sharpie marker and colored the thread dots on the front black. Several washings later you still can't tell, so in my book it worked.
Just promise not to tell the quilt police on me.