Color slope S′(B − R) as a function of phase angle α. The left columns correspond to silicate particles of m = 1.6 + 0.0005i, and the right columns correspond to silicate particles of m = 1.6 + 0.01i in red light. The different rows correspond to a different increment of the imaginary part of refractive index ΔIm(m) in blue light ΔIm(m) = 0 (top), 0.1 (middle), and 0.2 (bottom). The organic component was set to m = 1.957 + 0.341i in red light and m = 1.855 + 0.45i in blue light everywhere. The blue and brown curves demonstrate the color slope of the Mg-rich silicate particles and organic particles, respectively. The magenta curves show the result when they are mixed.