I think you mean the general symbology like in old OF4.x days?
Like the frame around the MFD, which shows you the SOI?
If yes, I don't think you can change it in a way of the "normal" configuration.
You can only choose monochrome MFD's or green AG-Radar-Mode over the configuration-file.
Nothing to see about changing everything to green.
Maybe it is possible to edit the graphic itself inside the game-folder?
But I have no clue, how to do that - or if it is possible.
Hopefully any other can give you a helping hand...