code: def _process_glsl_template(template, colors):
      
      for i in range(len(colors) - 1, -1, -1):
          color = colors[i]
          assert len(color) == 4
          vec4_color = 'vec4(%.3f, %.3f, %.3f, %.3f)' % tuple(color)
          template = template.replace('$color_%d' % i, vec4_color)
      return template
docs: Replace $color_i by color #i in the GLSL template.