Indigo is one of the oldest natural textile dyes. It was known and used throughout the ancient world, in Europe, Asia, Africa and the Americas. Indigo produces a dark stable blue, which we would call navy blue. There are examples of textiles dyed with indigo that are thousands of years old where the color is still a dark rich blue.
Natural indigo was replaced by a synthetic aniline based dye around 1897. Today, almost all textiles world-wide are dyed using aniline dyes.
A simple blue and white color scheme for a quilt has been popluar in America since colonial days. It is very difficult to date blue and white quilts. One can determine if the fabric was dyed using a synthetic aniline dye which means the quilt was made after 1897. But, althought it is rare, natural indigo is still used today, so a quilt made with natural indigo dyed fabrics may not necessarily date to before 1897.
Here are five blue and white quilts. Based on other clues, such as print pattern, batting, block pattern, border style, binding and quilting motifs, I believe they were all made between 1880 and 1940.