Trouble

Thank you all! I'll have to try this out. As a matter of fact, the photo's were taken with a smartphone and it was only later I realised that they can be combined. Great!

I made two photos of both sides of the isle of Arran of which I want to make one (panoramic view of the complete isle). I took these photo's in one and same minute but still ... The photo's match very well in height etc. but I don't know why but the colours are different (the second one being darker). How do I make the colours of the sky, the sea and the isle match?