This issue has been resolved and fixed for the next release 10.7.
Another easier workaround would be to change the resampling method on the image display. Right click on the image in the Table of Contents. Go to the layer properties. Under the Display tab, change the 'Resample during display using' to Nearest Neighbor. This resolves the issue and not allow current users to create a copy of the all the rasters (using Copy Raster) when using large amounts of data.
対処法
Create a copy of the raster (using the Copy Raster tool), make sure to check "Colormap to RGB". Keep the rest of the parameters as default.
Add the copied raster to a mosaic dataset. The color map is not lost by building footprints on this mosaic dataset.