Anyone standing on the hard shoulder on French motorways should be wearing a high visibility vest/jacket according to French driving regulations.
It is a minimum requirement that at least one Hi Viz should be kept in the vehicle in the event of breakdown etc for the driver. The vest should be inside the cabin of the vehicle not stored in the boot or in a roof top box etc as you should be able to reach it and put it on before getting out of the car.
But the law clearly states that every individual stood on the hard shoulder should be wearing a vest, so ideally you need one for every passenger in the car.
We put one Hi Viz Vests into our "All In One Travel Kit" and individually and you can buy them here as a single item or as an addition to the All In One Kit for extra passengers.
So when driving in France you'll need a Hi Viz Vest for you (the driver) but the passengers are also required to have one.
On the Euro Motoring website a single Hi Viz is £4.95 (Correct 12th June 2022) but you can buy additional ones at a discount.
If your are the typical 2 adults, 2 children then Euro Motoring have a family pack that has you covered.
There is no official colour that you must have. The ones most commonly used are the yellow ones but if you have an orange vest that will be fine assuming it has the correct EU standard reflective strips on them.
More than the colour the reflective strips are the most important element but standard yellow is what I would use.
As long as the vest is up to BS EN 1150 standard then it will be fine. That covers you for "private use".
You only need BS EN ISO 20471 standard hi viz for trade/professional use. This is far more durable high viz workwear.
Not while driving no. Only if you have reason to stop and get out of the vehicle on the hard shoulder on the Autoroutes (Motorways).
Whatever type of road you are on you should put your Hi Viz on if you have broken down or been involved in an accident.