The performance in judging values in a univariate map encoded using five different color scales was tested in eleven subjects. Digital elevation maps (DEMs) were encoded using: 1) an RGB gray scale (RGB), 2) a gray scale based on CIELAB L* (L*), 3) a L* scale with an added red hue component (Red L*), 4) an L* scale with continuous hue change (Spectral L*), and 5) a gray scale based on luminance (Luminance). Performance was tested using an Evaluation task and a Production task. For both tasks judgments were made both with and without legends for all five encoding schemes. The results show a significant effect of choice of encoding scheme, the presence or absence of a legend, and an interaction between these two factors. Performance with a legend was significantly better than without one. The Spectral L* scale led to the best performance while Luminance encoding was the worst. This experiment is a first step in using quantifiable psychophysical procedures to evaluate the effectiveness of different color encoding schemes on the interpretability of multidimensional graphical images.