In herbicide-selectivity experiments, response can be measured by visual inspection, stand counts, plant mortality, and biomass. Some response types are relative to nontreated control. We developed a nondestructive method by analyzing digital color images to quantify color changes in leaves caused by herbicides. The range of color components of green and nongreen parts of the plants and soil in Hue, Saturation, and Brightness (HSB) color space were used for segmentation. The canopy color changes of barley, winter wheat, red fescue, and brome fescue caused by doses of a glyphosate and diflufenican mixture, cycloxydim, diquat dibromide, and fluazifop-p-butyl were described with a log-logistic dose–response model, and the relationship between visual inspection and image analysis was calculated at the effective doses that cause 50% and 90% response (ED50 and ED90, respectively). The ranges of HSB components for the green and nongreen parts of the plants and soil were different. The relative potencies were not significantly different from one, indicating that visual and image analysis estimations were about the same. The comparison results suggest that image analysis can be used to assess color changes of plants in response to some herbicides and may have the potential to provide an objective measurement of symptoms.