Hello, could someone help me to change only the red color of the barrier to replace it with white. Thank you so much.
You need to select a different Material.
Click on the drop-down menu for the field “Materiau de la barrier” and type “white” and you should get at least one material matching that you can select.
Or maybe you need to type “Blanc” or similar. 
It’s not the same barrier, here it simply makes a white wall, except that I wanted the same barrier but in white color
I think you’d need to make your own translucent material then (based on white instead of red), and I don’t have experience with that.
Here’s an example where I picked a different Epic translucent material - but there only seem to be a few to choose from.
OK, thanks a lot
Or maybe you need to type “Blanc” or similar.