What color thread was originally used?
The flag makers during the time of the Civil War used any color they had. If you look at original examples, you will find red, black, white, grey, blue.. etc.. etc… It doesn’t seem to matter although some took great pains to match colors. Most did not. We like using the neutral colors. Gray and light brown are good natural colors and don’t accentuate the stitching as much. It is just our preference.