Use The Radial Filter

Click on the ‘Radial Filter’ tool to exit the ‘Graduated Filter’, and then click once on the minus icon next to ‘Temperature’ to get a setting of -25 and zero the other sliders. Change this to about -10, and then drag out a sausageshaped oval selection over the misty background. The pale blue colour will be subtly enhanced. Increase the ‘Highlights’ slider to brighten the mist and, if you want a stronger effect, right-click inside the Radial Filter’s outline and select ‘Duplicate’.