If you study the picture below, you will notice that the sand is not all the same colour. There appear to be three colours.
Ignoring the footprints, seaweed and stones, we can see some very dark sand, some browny-beige sand and some very light coloured sand.
See if you can come up with an answer to explain the three main colours, why we see them where we do and what any of this has to do with navigation.
I gave a full answer and explanation in my Natural Navigator News email newsletter. You can sign up at the bottom of the page if you haven’t already.