I will try to get it to some local body shop and see whether they are able to match the colour. Should I get something Like a RAL value, I'll be sure to report it here. Would be nice if we could have some sort of database of Motobecane paint colours from various periods and modern equivalents...

And an update on the frame identification. When it comes to seat posts, I have tried 27.2mm, 27mm and another 26.8mm. 27.2 is no go. 27mm will go in and can be taken out, though the fit is a bit tight. Not overly so, it doesn't have to be forced. Another 26.8mm is more or less as the current one - will go in fairly easily but not drop in or silde in under its own weight and can be taken out fairly easily. So probably the correct diameter would be somewhere between 26.8mm and 27mm.

Looking at the photos of the steerer tube I have noticed an additional stamp I didn't see before. There is "NERVOR" stamped above the for race, very faintly. Took additional photo (below). I'm aware of Nervar and Nervex, but never heard of Nervor. I've seen some other posts mentioning it (in all the photos I've seen so far it's amuch bigger stamp and more pronounced than on mine), but nothing conclusive so far. I guess need some more research into this.