Plot[{Sin[x] - (x - (1/6) x^3), 1/120, -1/120}, {x, -1, 
        1}, PlotRange -> {-1.2/120, 1.2/120}, 
      PlotStyle -> {RGBColor[0, 0, 0], RGBColor[1, 0, 0], 
          RGBColor[1, 0, 0]}]