how about you render/cut the sky from that image and then add your own magenta sky? Mountains are fairly easy to make/come up with. There's several mountain renders online and you can edit the colors manually.
Well it depends on what kind of image editing program you're using. Look up rendering in whatever program you use and do it on the sky. It should be pretty easy on that image, or you could even manually apply pink/green/any standout color to the sky and then use a magic eraser tool to remove it, whichever makes you more comfortable. After you've rendered/cut out your sky you can find another sky on google/deviantart/etc, to replace the old one. I assume you know how to change the color of something within your image editor, if not you should really spend more time practicing using your program, and consider watching some tutorials.
