IN a recent issue of NATURE1, Dr. W. D. Wright has given a very clear and interesting account of recent work in the direction of commercially practical application of measurement in the matching of colours, and in their analysis or synthesis. On the practical side the first steps were taken independently by Helmholtz and Maxwell in the employment of spectrum standards—always reproducible. By means of these, other standards, more normally attainable, more readily and simply usable by scientifically untrained workers, can be brought into employment.