Yes, this is true. Raster layer symbology, drawing properties, are not supported in the Mobile Package. You could create a Map Tile Package of your TIF, or export a new version of it with the desired colors ' burned into' the raster file.
This is something that we have on our list to support in the future. Really appreciate your feedback on this, it is the requests of the User Community that helps us prioritize the the work that we do.