A white, yellow of ice blue Lycra or Nylon suit may become see through especially when wet because the fibers themselves become transparent when wet yet they may still filter out UV light.
A tan through fabric is a very fine mesh net. They are usually printed in very bright and dark colours with energetic patterns.
here is the current Kiniki range here in the UK:
https://www.kiniki.com/collections/2...through-briefs
Unless we are very intimate with someone we usually see them from a distance, the tan through bikini looks like normal Lycra or Nylon from a distance but from up close we'd realise it is a fine brightly coloured and patterned mesh and it is unlined.
If we hold up dry white Lycra fabric to our eyes we will see light and dark but no details, but if we hold up tan through fabric to our eyes the illusion breaks, we ignore the colour and pattern of the fabric and see the view before us through a mesh. When the sun shines you will be tanned through the holes in the mesh, while the mesh gives the impression of being dressed.
In the story The Emperors New Clothes it is the small boy who sees through the Emperor's clothes and similarly a small child whose eye line is level with your loins may break the illusion of colours and patterns and see you naked.