anchor.diff:        num real = pixelToReal(x);
         int count = probe(real, imag, maxIterations);
   
  -      String color;
  -      if (count == maxIterations) {
  -        color = "#000";
  -      } else {
  +      String color = "#000";
  +      if (count < maxIterations) {
           color = colors[count % colors.length];
         }
   
         if (color != prevColor) {
           if (prevColor != null) {
  -          assert(x > left);
             context.fillStyle = prevColor;
             context.fillRect(left, y, x - left, 1);
           }
  
positive.code:         left = x;
        }
      }
      assert(width > left);
      context.fillStyle = prevColor;
      context.fillRect(left, y, width - left, 1);
    }
  
negative.code:     this.height: 400,
      this.colors: const [
        "#f10","#e20","#d30","#c40","#b50","#a60","#970",
        "#880","#790","#6a0","#5b0","#4c0","#3d0","#2e0","#1f0"],
      this.onClick
    });
  
  