Creating material for a tile based map

So i am trying to achieve this effect with borders having intensive color and make it kind of fade into the land with materials and material functions.
Im thinking that i should use a gradient and material functions to get something like that but i have failed so far. Any directions as to how that can be done will be much apprecieated.
Also im wondering how i can make a material display on not whole mesh? Or to do that i would have to make a specific texture for that mesh?

Someone? D:

Assuming your doing the same 2D style, you could make those borders in a sprite sheet like how the tile sheets are done(I believe UE4 calls them FlipBooks). Then just draw the border sprites on top of the map.