Well it just so happens I have both of these paints in my stash. (From the time I sort of accidentally won an ebay lot auction of over 50 W&N paints….) I also have a Cotman 12 half pan set that I got nearly 3 years ago, and it included the French Ultramarine, so it’s possible that’s the same one?
I grabbed a little of each and painted it onto the back of a failed painting on 140# cold press to compare side by side for you. I know the color won’t be quite as true to life since it’s on digital screens, but maybe it helps some? They’re both made with the same pigment (PB29) so there’s not a ton of difference IMHO. PB29 is a favorite blue of mine because of the granulation. French Ultramarine on left, Ultramarine Green shade on right, in case my terrible handwriting isn’t clear.