As color digital printing expands into the business and consumer markets, the importance of “color accuracy” has increased. As a result, more and more people have had to become familiar with concepts such as color difference equations and ΔE*. While many of the concepts of color measurement are clearly explained in several current books, the myriad practical issues that contribute to color measurement error are seldom discussed. This leaves the practitioner of color measurement with tools for measuring color but little understanding of the key variables that affect the measurement process.This paper examines critical factors affecting accuracy in color measurements and sheds light on issues involved in integrating color measurement into on-line or automated applications. The focus of the paper is to bring out key calibration issues, including frequency calibration, gain adjustment, dark reference and light reference. The repeatability and accuracy of color measurements are examined. Key sources of error are investigated, and suggestions are made for reducing sensitivity to them.