> Is it really impossible for the cone response to a compound color to match that of any single wavelength? Yes. Look for a "chromaticity diagram" to see the

> Is it really impossible for the cone response to a compound color to match that of any single wavelength? Yes. Look for a "chromaticity diagram" to see the colors we can perceive. It is a convex shape, like a truncated parabola, and the pure colors are on the edge of the parabola curve. Any time you mix two pure colors, you end up inside the parabola instead of on the edge. Conversely, any color on the inside of the parabola cannot be a pure wavelength and must be a compound color. There are a lot of colors we call "yellow". Some are pure colors and some are compound colors. The ones that your monitor display are compound colors that cannot be found on the spectrum. A decent monitor will represent brilliant yellow colors fairly well. This is due to the low curvature of the edge of the chromaticity diagram in the green-red range, which in turn can be ascribed to the similarity of the response curve for the L and M cones in the eye, compared to the S cones. However, brilliant turquoise and aqua colors won't show up on your monitor.