This is a very timely question for me. I did FMQ on a tablerunner yest. using an off white thread on top & a brown in the bobbin. No matter how much I practiced on a scrap sandwich & kept changing the tension I still ended up with a bit of brown coming up to the top. I was just sick since the runner belonged to somebody else who doesn't do FMQ. I felt I ruined her runner but she was happy with it.
On a tute video I watched yest. the person said to really crank the top tension up to a very high number. Like 8. I didn't think to go that high.
I'm anxious to see how others manage this.