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Clicking on the 'voir conditions' ("view conditions") to the right of each of the prices should give you details of the differences between the two fares.
Presuming that you do not speak French, a better idea is to instead access the English website, which can be selected by clicking on the English flag at the bottom of the voyages-sncf.com homepage.
Specifically to your example, there appear to be 2 sets of conditions for each of the options, due to your booking being on 2 different services - the first on Thalys, and the second on TGV. The description of the conditions are :
For the Orange option :
Thalys NO-FLEX : Ticket cannot be exchanged and is non-refundable.
TGV Prem's : Ticket cannot be exchanged and is non-refundable.
For the Green option :
Thalys SEMI-FLEX : Ticket can be exchanged once at no cost up until the day before departure. Subject to a penalty of 50%, the ticket is refundable before departure and up to one hour after departure at a departure station in France. Tickets will not be exchangeable or refundable after departure. FREE WIFI
TGV Prem's : Ticket cannot be exchanged and is non-refundable.