code: protected void fillTile (
          Graphics2D gfx, int tx, int ty, Color color)
      {
          Composite ocomp = gfx.getComposite();
          gfx.setComposite(ALPHA_FILL_TILE);
          Polygon poly = MisoUtil.getTilePolygon(_metrics, tx, ty);
          gfx.setColor(color);
          gfx.fill(poly);
          gfx.setComposite(ocomp);
      }
docs: Fills the specified tile with the given color at 50% alpha.
  Intended for debug-only tile highlighting purposes.