Well, I'm glad to hear there is hope. I have ordered some bottom line 60 wt thread in a light gray and a darker gray. I will work on a sample as you suggested and try and keep a close eye on my tension. I appreciate your suggestions. They are most helpful.

It's your quilt, do what you want. I have used different colored threads before with no big problems. Sure. occasionally the tension will pull one thread one way or the other, but it is not objectionable to me. If you are entering a show, a judge will probably say something. But for daily use, no one will ever notice.

Most of the time I use different threads on top & backing. I’ve never had problems

The others have had good advice. I only want to add that you should use a new needle, a quilting needle or a topstitch needle. If you do get a poky or two, change your needle again.

Yep, I think with experience you will get a good idea on what works for you. I am mainly a quilter who makes quilts to be used not show quilts so I don't get too stressed out if my tension is a little off or if the bobbin thread shows on top every once in while. My main concerned is that the quilt will hold together with use and washing. You also may want to wash your practice piece to get an idea of how the washing itself will change how the stitching looks. I find often, although I can see a bit of the bobbin thread on top whether I use matching threads or not, when it is washed, the bobbin thread on top becomes less visible. I know how to adjust my tension but find sometimes it is just so much less stressful to use matching thread. I do know long arm quilters who just about always use grey or cream on in the bobbin unless they are doing a white work quilt then they use white of course. I wind my own bobbins and usually use the same thread top and bottom. That works for me.

If I'm using a dark color on the top and white/cream on the back, and if thread occasionally show thru on the top, I simply color it with a black magma pen.

I also think you can do it. I do all my own FMQ on my domestic (Janome) machine and it works for me. Although, I do try to use a backing that is not a solid color as then the whoops don't usually show. Like others have suggested use a practice piece until you get what you like. Good luck!

I've never been able to do it without the opposite threads poking through. If I were going to try, I'd use the thickest wool batting I could find to give me more room in the middle.

I've done it many times. I'm not great at the quilting part, so want my thread to blend in. I generally use whatever color matches the back in the bobbin and Gutermann invisible on the top when I'm dealing with color issues. I use vintage sewing machines, so they aren't really picky about thread. I've never tried invisible thread in the bobbin, though.

bkay

I use whatever color thread matches my backing fabric for the bobbin and whatever color disappears into the top or accents it. Choice is the perfect answer, do what suits you. That being said tension absolutely plays a large part if you’re using different colors.