Thanks for the reply, but it doesn't work.
I have tried [node size - 1] and many other index values.
As long as the index value is larger than the max index of ROI, there always

-- Error SUMA_IsCmapOKForLabelDset (SUMA_Color.c:4273):
Have 2 unique values,
have no colormap big enough for this
-- Error SUMA_CreateCmapForLabelDset (SUMA_Color.c:4223):
Provided cmap is no good
-- Error SUMA_dset_to_Label_dset_cmap (SUMA_Color.c:4321):
Failed to add colormap
-- Error ROI2dataset (SUMA_ROI2dataset.c:496):
Failed to make change

What can I do to deal with "have no colormap big enough for this " ?
Thank you very much!