Here's a little mod that changes the stock colour of the chart. The colour of the land, water and grid lines have been changed to match an example Kriegsmarine chart posted on the fleet boat thread.
The first chart only shows shallow depth, to try to match the chart only showing depths round the coast. The second chart scheme shows all depths, with a different from stock colour, to give it a bit more definition, as I had trouble seeing the depths clearly. The depth colours are inverted, as it appears naval charts show the shallows as dark blue and the deep as light blue or white.
Chart Colour Scheme #1.
Chart Colour Scheme #2.
Thanks to Bosn and DS for the inverted shallow colour idea, Mikhayl for the grid line colour change info and LukeFF for the example chart.
There are different colour schemes available on the fleetboat mods thread, with terrain detail for the land as well if anyone is interested in those.
You can get the above from
http://files.filefront.com/Kriegsmar.../fileinfo.html