Bobbin & upper thread color
 

When you quilt, do you always have the same color thread in the bobbin as you do on the spool? I am doing a quilt right now where the top is white, the back is black, so I have a colored thread in the spool and black thread in the bobbin. My tension seems fine but I still see black through the needle holes. I'm hoping it will close up once it goes through the wash, I am starting to think I may use the same color in the bobbin as on the spool so I don't have this problem.

I just finished a quilt on the longarm using a dark green in the bobbin and off-white on top. I was a little worried about it, because I know there are some big name longarm quilters who will only use the same color top and bottom, but in this case the dark thread didn't poke through to the top, and the light thread doesn't show on the back. If you're only seeing the dark thread through the needle holes it should be fine after it is washed, but if the dark is actually being pulled through to the top then you will need to adjust your tension.

If you are doing free motion quilting, the bobbins thread can pop up even if you tension is OK. I know in the beginning when Long Arm quilting machines became popular, many of them required the same color in the bobbin that was to be used on the top. I quilted with my Bernina so with straight stitching, I had no problem. But when doing free motion, I always tried to keep the colors similar so that if the bobbin happened to pop up occasionally, it would not show. It is near impossible in FMQ to be precise with exact stitch length. That is why the stitch regulators became so popular when they first became available.

I often use a different colored thread in the top and bobbin when machine quilting. It could be that you are seeing black in the needle holes because your needle size is too big for the weight of thread you're using and what you might actually be seeing is the backing fabric reflected back through the holes. To check this, look through a magnifying glass; that way you can discern whether it's thread or the black fabric on the back.

Do what pleases you .... however, a coloured thread on the black could be quite effective and might help brighten the black back a little.

Many opt for same colour top/bottom for the easy route, for less need to get the tension set so the threads meet in the middle of the sandwich. If this is what you want, then make a test sandwich, replicating your quilt and adjust til you get it to where you are happy.