output of pcd.crop_point_cloud btf_print preview not show color info

[HowcanoeWang]

reproduce:

>>> pcd
                    x            y        z  r    g    b        nx      ny      nz
        0  368057.379  3956051.919   96.685  177  177  161  nodata  nodata  nodata
        1  368057.405  3956051.796   96.689  144  141  122  nodata  nodata  nodata
        2  368057.403  3956051.803   96.687  141  138  118  nodata  nodata  nodata
      ...     ...          ...      ...      ...  ...  ...     ...     ...     ...
123187743  368133.04   3956019.956   96.643  88   107  78   nodata  nodata  nodata
123187744  368132.9    3956019.851   96.663  114  149  123  nodata  nodata  nodata
123187745  368132.895  3956019.882   96.66   119  115  99   nodata  nodata  nodata

>>> grid_pcd = pcd.crop_point_cloud(grid[grid_id])
                 x            y        z  r       g       b           nx      ny      nz
     0  368065.365  3956052.669   96.562  nodata  nodata  nodata  nodata  nodata  nodata
     1  368065.346  3956052.665   96.572  nodata  nodata  nodata  nodata  nodata  nodata
     2  368065.355  3956052.668   96.566  nodata  nodata  nodata  nodata  nodata  nodata
   ...     ...          ...      ...      ...     ...     ...        ...     ...     ...
215024  368067.917  3956051.22    96.736  nodata  nodata  nodata  nodata  nodata  nodata
215025  368067.896  3956051.331   96.841  nodata  nodata  nodata  nodata  nodata  nodata
215026  368067.905  3956051.275   96.722  nodata  nodata  nodata  nodata  nodata  nodata

>>> grid_pcd.colors
array([[ 42,  29,  20],
       [ 62,  52,  46],
       [ 64,  50,  44],
       ...,
       [ 98, 112,  99],
       [ 69,  74,  70],
       [ 56,  53,  46]], dtype=uint8)

>>> grid_pcd._update_btf_print()
                 x            y        z  r    g    b        nx      ny      nz
     0  368065.365  3956052.669   96.562  42   29   20   nodata  nodata  nodata
     1  368065.346  3956052.665   96.572  62   52   46   nodata  nodata  nodata
     2  368065.355  3956052.668   96.566  64   50   44   nodata  nodata  nodata
   ...     ...          ...      ...      ...  ...  ...     ...     ...     ...
215024  368067.917  3956051.22    96.736  98   112  99   nodata  nodata  nodata
215025  368067.896  3956051.331   96.841  69   74   70   nodata  nodata  nodata
215026  368067.905  3956051.275   96.722  56   53   46   nodata  nodata  nodata