Supposedly the closest colour you will get to the modern Marine Nationale colour is RAL7040.
Here is a photo of my (badly) built ETN-90 for my FLF Guepratte painted in RAL7040:-

I know it is gloss but my reasoning was that it would show up better behind the stealth screens.
I spent hours if not days agonising over what colour to paint the model and I found some pictures on the internet of Guepratte in Monte Carlo harbour and discovered, in closeup, that the ship is actually a patchwork of about five or six different greys.
Photos, taken invariably in the Med in brilliant bright sunshine, give the ships (certainly the FLF's) a very light, almost blue shade, but I am convinced that this is a trick of bright sunlight and bright blue sea. Whereas the photos of the Guepratte at Monaco in the rain show it is actually much darker. plus, it has a flat, almost rough look.
Eventually I went with good old Plastikote grey primer and I think it looks just about right:-

In case you are interested the real paint code for the ships is:- M29 Joint NSN 8010 14 4419203
All the best
Sandy