// result can be used in coloredTextToTextPane
static L lineCompedSingleLevelsAsColoredText(LineCompedSingle<Char> lc) {
  // each matrix element is the symbol starting position for the character+1 (or 0 for empty)
  int[][] rows = renderLineCompedSingleLevels_raw_v2(lc);
  S text = uncompressLineCompedSingle(lc);
  printVars(+rows);
  int n = l(first(rows));
  new L out;
  forEach(rows, row -> {
    var color = Color.white;
    out.add(color);
    var lastSymbol = 0;
    for i to n: {
      if (row[i] == 0) {
        if (color != Color.white) out.add(color = Color.white);
        lastSymbol = 0;
        out.add(' ');
      } else {
        if (row[i] != lastSymbol) {
          color = color == Color.yellow ? lightBlue() : Color.yellow;
          out.add(color);
          lastSymbol = row[i];
        }
        out.add(text.charAt(i));
      }
    }
    out.add("\n");
  });
  ret out;
}