I just figured out a way to do this using an unmanaged raster catalog. As stated in the earlier replies, create a symbology (e.g. a color map) that will cover all possible values. Use a script to apply this to all the rasters. It can take a long time, but can run in the background while you get other things done.I used the following simple script to apply a color map to a zillion grids within a workspace. Modify as needed:## Add color map to DRGs
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import arcpy
from arcpy import env
# Set workspace
arcpy.env.workspace = "C:/your_path_here"
# Get list of grids
rasterList = arcpy.ListRasters("*", "All")
for raster in rasterList:
# Assign colormap using clr file
arcpy.AddColormap_management(raster, "#", "your_symbology_file.clr")