The InverseTable module is a utility module designed to aid in the task of manipulating colours in palettised modes. Specifically, it will generate lookup tables which can be used to convert palette indices to and from RGB values.
ColourTrans provides similar functionality via the ColourTrans_ReadPalette and ColourTrans_GenerateTable SWIs. However the differences in the implementations and the APIs make the two modules suitable for different purposes.
One major limitation of InverseTable is that it only works with 256 colour palettes. If you require translation tables for 2, 4 or 16 colour palettes then ColourTrans should be used.