code: def set_axis_color(axis, color, alpha=None):
      
      for side in ('top', 'right',  'bottom', 'left'):
          spine = axis.spines[side]
          spine.set_color(color)
          if alpha is not None:
              spine.set_alpha(alpha)
docs: Sets the spine color of all sides of an axis (top, right, bottom, left).