Color is an effective and commonly used channel for displaying data in
surface visualization. However, color is affected by shadows and shading,
which convey depth and shape on surfaces. The human visual system has evolved
constancy mechanisms for identifying color under varying illumination
conditions. Lightness constancy allows people to accurately perceive colors
in real shadows; however, its effectiveness in surface visualizations is not
well understood. We report a series of initial studies that confirm the
existence of lightness constancy effects on molecular surface renderings. We
evaluate common design decisions to show how choices of attenuation, color
ramp, and shading model impact viewers' abilities to accurately identify
colors on molecular surfaces rendered with ambient occlusion. Our findings
lead to a set of generalizable design implications for effective surface
visualization using color.