Martian dunes. ” The image was taken using the red-green-blue filter on the camera, giving the sand a blue appearance.” So, not true colour. More like storytelling.
But there’s a specific incident in (Frank) Herbert’s life that seems to have set him off in this direction. He made his living as a reporter before his fiction writing took off. In 1957, when he was in his 30s, he was sent to write about a system of dunes in Oregon that were migrating and therefore endangering towns.
The US Department of Agriculture were using grasses to try and stabilise the dunes. And Herbert had been really struck by this – modifying an ecology to achieve a goal, as opposed to using technology, such as big fences.