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The problem is, that I only can estimate from my SIGMA RAW experience to optimise here. Would be nice to have the RAW-File?! If you would like me to do exact work, send me a PM ... you will get my mail adress then.
1) White balance ...
you used ATM-WB ... that is what I do in most cases as well. In many cases this works perfectly ... in this case I see a yellow tint. This sometimes happens because your SD tries to compensate the blue sky.
Change the White Balance in SPP 2.5 to 8C+8M (using the colour-circle)
"C" means cyan and "M" means magenta
2) Your shot is frontlight! So, the bright sky in the background slows down exposure. You could have corrected exposure when taking the pic. If you speed up exposure too much, the sky will lose colour ... appear just white ... no solution as well!
Change the Fill light slider to values between +0.3 up to +0,8 to fill light into the shades. Watch the sky now carefully! If it loses brillance then change the lights to say (+0,5 -+1.0) If the pic then looks too flat or lifeless reduce the shadows a bit. Better do not change contrast using the contrast-slider.
I can correct the WB and lighten the pic ... Fill Light only can be done with the RAW-file