National flags might seem like a riot of colour, but there is one colour that you will almost never see on a flag and the reason comes down to the ancient trade in rare sea snails.

Yellow flags have been raised on a beach in Tenerife to warn tourists about dangerous marine life that's been spotted in the waters, as well as a purple flag ...

When visiting Spain, especially along the coastline, it is essential to educate yourself on the meaning of the different warning flags. Article continues below The most obvious is the red flag.

Yellow flags have been raised on a beach in Tenerife to warn tourists about dangerous marine life that's been spotted in the waters, as well as a purple flag ...