code: def background_color(ax, color, scale, zorder=-1000, alpha=None):
      """Draws a triangle behind the plot to serve as the background color."""
      vertices = [(scale, 0, 0), (0, scale, 0), (0, 0, scale)]
      vertices = map(project_point, vertices)
      xs, ys = unzip(vertices)
      poly = ax.fill(
          xs,
          ys,
          facecolor=color,
          edgecolor=color,
          zorder=zorder,
          alpha=alpha,
      )
      return poly
  
file_path: python-ternary/ternary/heatmapping.py
imports: import functools
  import numpy
  from matplotlib import pyplot
  from .helpers import unzip, normalize, simplex_iterator, permute_point, project_point
  from .colormapping import get_cmap, colormapper, colorbar_hack
label_desc: Use image node_id 12 for calling a global function with example usage: background_color(ax, color, scale, zorder, alpha) and returns: poly