I am not aware of power types and wiring standards in France, so I can't offer too much advice. I would, however, recommend that you call a smaller hardware store and ask them for the wiring standard. They should be able to tell you what color wire goes where.

Is it a polarized plug? Is one of the prongs fatter than the other?

You could disassemble a power plug on an item you don't want and figure it out from that.