Hi,
At the moment this is not possible, but has been a regular request.
The release in January will address this - for example, all track point colours in the define map view will be based off the same depth range.
The big change is the move to vector isobaths, which will eliminate the need for a raster background in AT5 maps (although the option will remain for those you want it). Depth areas will be exported as polygons, which can be filled in specific colours for display in the finished map (AT5 or KML). The User Map will become (more or less) WYSIYWG for finished AT5 maps, with plenty of flexibility to colour depth ranges in whatever way you like (as well as some automatic palettes).
You just have to wait about another month :)