Why does slope data in a mobile map package lose its colorful symbology? The slope map was setup in Pro to use different colors for the slopes. After the MMPK was added into Field Maps, it showed up black and gray.
The ArcGIS Runtime (which Fieldmaps is built with) does not support 'symbology' (layer symbol properties) that is applied to raster (image) data. Raster formats are rendered in display as they exist. After rendering your imagery in Pro via symbol settings, you could export the raster to a new file (or create tile package .tpkx)... to 'burn in' the symbol choice in a new raster... as a workaround.
This deficiency in the ArcGIS Runtime is not good. Any hope it might be in a near term roadmap? Duplication of imagery to preserve symbology is a waste of time and storage space.