Chosing colors to quilt with, advice wanted.
 

I am almost finished with my second quilt, all I have left to do is to quilt it and its done. Its a basic quilt with red white and blue squares, and a denim back.

I plan on quilting it in straight lines, but since the colors are so different, which ever color I chose will show up easily on the two other colors on the quilt.

you could always use a grey, they seem to blend best. I do grey on a lot of mine. Or go white so it stand out a bit.

It is OK that your quilting will show. Although I would normally default to white or light gray thread, I would consider using dark blue in this case since your backing is dark blue. An alternative is to use white thread on the top and blue on the back/bobbin, but I have always worried about using two different thread with that much contrast in case the darker color pops through on the front in the event your tension is not perfect. You might try a sample sandwich piece with scraps and see what happens with a light color on top and darker on the bottom and see if you like the result.

I would chose a light grey or white.

Wish you had posted a picture. When I test what thread to use, usually I just doodle the thread on the quilt top and see what thread color looks the best.

I intensely hand quilted a red, white and blue quilt with red, white and blue variegated thread and was very pleased with the result. In fact it won first prize at a local quilt show. I think it will depend on how much you would like the quilting lines to stand out.
Anne