Color shades have several different causes. The printer may use a different ink; in the early days, inks were made up in batches as needed, and were rarely consistent. In such cases, the shade provides information about when the stamp was made, and possibly even identify a particular printing. Extreme variations may be considered color errors; for instance, the 4c value of the US Columbian Issue of 1893 was normally printed in ultramarine, but a handful were printed in blue, a shade with distinctly more green; these are worth in the US$10,000 range instead of the usual $10.