In the original shot the orange tinged flash (1.5CTO gel, 1/64 power, grid spot, camera right) illuminates the model wind turbine with a tungsten coloured glow. The overcast sky outside looks as it did when the shot was taken.
The image on the right shows the benefit of Mr Hobby’s advice: If you set the camera to Tungsten white balance, the colour temperature of everything in the frame is lowered. The warm orange light is cooled to bring it back to the colour of daylight while the already cooler sky is lowered to a deep blue.
Not the most exciting subject I’ll admit, but its a great effect and I can’t wait to try it properly. By underexposing, and using sufficient CTO, you can create that just after sunset look virtually anytime you like.