I installed the latest version of Watch OS a couple of weeks ago and I've noticed a subtle difference in the standard weather complications. The cloud and wind icons sometimes appear in white as they did before, but sometimes they appear in yellow or blue.

 

I suspect the colours are likely to relate to UV index or upcoming weather conditions but I can't determine this with certainty. I have posed this question on Apple's community forums and several people have indicated that they also have this question but noone seems to have the answer. It's not even in the manual or any other support documentation.

 

Does anyone know the answer?