Wow that was fast and it seems to do the job well, I took a few similar pics and tried it :
Original pic :
Source : https://pixabay.com/fr/raisin-pourpre-vignoble-553462/
Quickly modified in Gimp :
Then using your Plugin to get the haldclut and applying the Clut on the 1st pic :
Now let’s try on similar images, original :
source : https://pixabay.com/fr/raisin-pourpre-vignoble-553464/
Now with the clut generated from the plugin :
And a last one :
Source : https://pixabay.com/fr/raisin-pourpre-vignoble-553463/
With the haldclut applied :
Looks very good !
Between the modified pic and the one resulting in the Clut applied on the original picture there is only a very light difference, very subtle but noticeable when you switch a few times from one pic to the other.
I used 100% for the setting “Influence of the color sample” not sure how much it can change with the different %'s, also used the 512x512 haldclut, need to try with the 4096px one, i’ll have to try more but overall it’s more than i expected, it’s marvelous 
Thanks a lot for this.