The cognitive strength of crosstalk in stereoscopic 3-D displays is investigated, and new quantitative analysis methods based on color difference and grayscale levels are developed. Unlike results using existing metrics, results by the new methods agree well with the perceived crosstalk strength in achromatic images with various levels of grayscale. The crosstalk in color images, which has not been studied before, exhibits interesting results in that the crosstalk metric based on the lightness difference expresses the best fit with the perceptual crosstalk when the intended image is black and the chroma value of the counterpart image is large, but the metric using the color difference works better when the intended image is not black. The new metrics reveal that the difference between active and passive 3-D displays is not as large as suggested by conventional crosstalk metrics, and the crosstalk in color images cannot be simply estimated by averaging the crosstalk of red, green, and blue subpixels. The new metrics will be useful in the development of new image processing technology and display technology for better image quality.