I used:
-curves to strenghten the contrast and colours
-shade/saturation tool(I'm not sure if it's the English name for it)to change the shade of the blue and to darken it.
-In the process of darkening blue nasty noise/artifacts appeared on the sky. To get rid of it, I duplicated the layer, applied Gaussian blur (radius 7px )to the bottom layer and removed the sky from the upper layer, using the soft-edge rubber on the mountain's edges to be more precise. The effect could be better, but I did my best ;-)
I'm sure someone else could make it more effectively, using professional methods. but I'm no specialist, mind you.
I hope you'll like the effect, please lest me know!
Greetings
Joanna