Backlight and Virga
The sun shining behind this cloud and precipitation below it cause this warm glow. The color is due to the low angle of the sun shining through the atmosphere, bouncing off air, water and dust molecules, which absorbs and refracts the cooler blue rays and allows the warmer yellow, orange and red rays to dominate, the same process that causes beautiful sunrises and sunsets. The light is shining through the cloud and rain, and just like trees backlit by the sun, the water droplets are illuminated from behind and seem to glow.
Nope, not done with the science lesson. Some of the moisture in the rain falling in the photo will evaporate before it reaches the ground. This kind of precipitation is called virga and is common where warmer, drier air is below the cloud. If you’ve ever been in the desert you may have seen rain falling from a dark cloud in the distance, but the rain disappears before it reaches the ground. If you can’t see it, that means it has evaporated. The whole dynamics of precipitation is more complex than one would think.
Photo location: Looking south-southeast at the end of Friday Harbor (the bay) near the shipyard.