I actually did that, and I was able to get closer to how I want it to look, but the thing is that I would like to have exactly the same color hex codes as I have on the website on the bottom (lighter corresponding to the bottom left part of the website, and darker to the stripe above it, and below the header). The best way to do that would be probably to invert the colors in the sky (darker pink - change to lighter pink, lighter pink change to darker pink) and just blend the left and right part of the header with the already existing background color (I would like to stick to that color too, thats why), that way it would look more natural, like the picture would be actually part of the header color etc.

I'll be trying different things, and see if I can get there or not (I actually want to use the same picture on different websites too, and just keep changing the background color of the sky, matching the new colors on the website - like dark blue, maybe black etc). Thats what I was able to get with the Hue method that you described: http://belerosemedia.com/

Thank you.