OK, this is what you do:
go to the folder Ubisoft/SilentHunterIII on your C drive
In that folder you will find a file called JSGME (which is a program. When you click on it to activate, it will create a folder called "mods" in that directory.
Into that folder place the four files you have decompressed:
"Blue U-boat Marker, green U-boat marker, gray U-boat marker, and Red U-boat marker."
Now when you click on JSGME again, all four mods will be listed.
Select the color (colour in Britten) that you want and then click on the > sign and the mod will be activated.
When you next start your game, you will have that color U-boat marker.
