Magical border sounds nice, good idea. But it was not intendet. As you said it is a problem with the transition but I am working on it. I'll post an update when I made some changes.
The brightness of the green border between the dark southern lands and the light green midlands bothers me. It is so bright against the rest of the map that it seems specially significant, as if marking a magical barrier or something, whereas I assume it is merely a transition between the two colorings. Maybe it's just me.