It's very unlikely that the forks will be French standard, certainly Italian.
The three standards you are likely to encounter are ISO (British), Italian and JIS: ISO and JIS threads are the same and Italian threads are so similar, that in practice all three are interchangeable.
However, the internal diameter of the crown race differs across each standard: ISO is 26.4mm, Italian is 26.5mm or 27.0mm and JIS is 27.0mm.
If your headset screws onto the Reynolds forks but not the Colnago pair, then I suggest you clean out the Colnago's threads: if they have been damaged, then you may need to get them re-cut.
I guess your forks have a 27.0mm crown, but unfortunately you have a 26.5mm crown race: you could either widen the crown race with emery cloth etc, or get a race from a JIS headset.
Probably best to check with Vernier callipers first though.