Thank you for fast reply. I installed Acme Fix Image plugin and fixed all medias. Also, I had already set the medias size in the media settings to the recommended sizes in the theme documentation (I read it before starting to customize my website and follow all the recommendations). The colors didn’t seem to have changed. my white still appear light grey although it is clearly white on the saved files like shown in my first post.
These images are uploaded in the Feature Section using the custom option.
Again, thanks a lot for your time.