Colour changes with light, weather and water conditions. Marketing photographs are not a guarantee of one exact shade.
There is no single answer. Heat, height, knees and balance matter. You can normally remain lower if the climb is unsuitable.
Talay Nai, as it is known locally, is a saltwater lake ringed by limestone walls in the middle of an island. It connects to the sea underground, which is why the colour does what it does. This is the photograph you have already seen of Ang Thong, and most day tours stop here.
Stairs and walkways take you up to the platforms. It is a much shorter climb than Koh Wua Talap, though the heat and a few steep flights still catch people out.
You look at this one, you do not swim in it. Follow the signs and your guide, and do not assume last year's rules still apply.
The view widens with every flight of steps, so keep going past the first platform. Use a strap and keep your hands free on the stairs. Step aside and let quicker people through.
Shoes with a back to them. Flip-flops slide on wet stone. Take water, a hat and sun cream even though you are only ashore a short while.
Choose a tour from the Ang Thong comparison and check that Koh Mae Ko appears in its current itinerary.