Readers of my books or this blog will be well aware by now that we should expect to find more puddles on the shaded southern side of tracks. And that this is also the side that holds onto snow for longest (see The Beast from the East).
The colour of mud is a more subtle example than either puddles or snow and takes a little more practice to spot. A warm dry spell after a lot of precipitation, rain or snow, is a great opportunity to start looking for this effect.
Which direction are we looking in the picture above?
Take the second, third, seventh and twenty-fourth characters of this post and you’ll have your answer.