The entire raster catalog is rendered based on the first dataset in the catalog. In this case it is using the associated colormap of the first dataset in the raster catalog. The first raster is determined by the first record in the raster catalog table.
Individual colormaps are not applied to raster datasets in raster catalogs at ArcGIS 8.3, or prior. In order to obtain better results in the display of the raster catalog, verify the raster datasets use the same colormap and rendering type as the first raster.
ArcGIS 9.0 is able to create geodatabase raster catalogs. Each raster dataset within a geodatabase raster catalog is rendered with the most appropriate renderer. When there are multiple colormaps, each raster member in the raster catalog is rendered with its own colormap.