Well, I was not satisfied with the Dark Sea Grey: in fact, I converted references for Gunze into Tamiya. The Dark Sea Grey from Tamiya sounds to me a little bit too "blue"...
So I decided to go to the Brussels Air Museum today, and to see the real aircrafts: Spitfire IX & Spitfire XIV.
As it seems, Spit KIV Dark Sea Grey is more lighter than the one I used - But it's not the case for the Spit IX, more similar to my paint...
And a French friend of mine said me that there were many variations in that paint, that was darker on the first Spits than on the latest ones...
So, I've decided to keep the colour I've used "as is"; I will just use pastels to lighten that paint...