Is it permissible to pray in a jilbab made of thin cotton that does not reveal the skin color, but might reveal the inner clothes if they are tight or short when bowing or under strong lighting?

If the jilbab does not reveal the skin tone to someone sitting near the person without intense scrutiny, then there is no objection to praying in it, even if what is beneath it (of clothing) becomes visible when exposed to light and sun. And if it is transparent but there is something underneath it that covers the awrah, the prayer is valid.