This paper is concerned with the development of perceptual colormaps for visualization. Colormaps are typically designed using algorithmic techniques and do not explicitly take into account the way in which the human visual system processes its underlying components. The typical colormap (the “rainbow” colormap), for example, maps data onto a scale of colors which varies in hue, brightness and perceived saturation over its range. In this paper we experimentally measure how hue, luminance and saturation scales represent magnitude information by constructing colormaps which trace carefully controlled paths through Munsell and L*a*b* color spaces, and comparing these results with colormaps designed using standard computer graphics methods.