Choosing a thread color for your quilting stitches is as important as the fabrics you use.
If you are new to machine quilting, try a thread color that blends or matches your fabrics well. When you match the thread color to the fabric your stitches won’t show as much. For a simple all over design try meandering. Meandering is just a larger version of stippling. Think of it like large puzzle pieces.
If you really want to show off the quilting stitches than use a thread in a color that is contrasting to the fabric color. This may be especially important when using decorative threads as a strong design element.
If you are not sure what colors will look best, do a sample quilt using the same fabrics and batting as in your quilt. Sample pieces are a good way to make sure not only the thread is right but also your tension and stitches are right. This is especially important when trying out a new quilting design.