Some of the explanations in Mathematica's Help files may not be as clear as we'd like them to be; here are a couple of possibly useful but less well explained options.

Plot[-1/(x^2 + 1), {x, -5, 5}, 
      PlotStyle -> {Thickness[ .01], Hue[0.5], 
          Dashing[{0.1, 0.05, 0.01, 0.05}]}, DefaultColor -> Hue[0.2], 
      Background -> GrayLevel[0.7]]

The Graphics option DefaultColor pertains to the color of all the adornments that are not part of the actual function being plotted (axes, tick-marks, numeration, labels, legend,...).

The Graphics option Hue[h,s,b] may be called with all three parameters (hue, saturation, lackness) or just the first one.

Plot[-1/(x^2 + 1), {x, -5, 5}, 
      PlotStyle -> {Thickness[ .015], Hue[0.25], 
          Dashing[{0.1, 0.05, 0.01, 0.05}]}, 
      DefaultColor -> RGBColor[0.2, 0.4, 0.6], 
      Background -> Hue[0.7, 0.6, 0.4]]