How to "blend" two+ textures at runtime?

Suppose I have a hexagon grid, and I have a grassland texture, and a forest texture. I want it such that depending on which one has "priority" for example the forest texture will slightly spill over from it's tile onto the adjacent grassland texture; I want them to "blend" nicely together to make the hex grid less obvious instead of it suddenly changing to a different texture arbitrarily.

One solution I've seen bandied about is assuming I have a single mesh to represent all of my hex tiles, somehow paint color information such that the color information will overlap adjacent tiles and being "blurry" where it overlaps (or decreased alpha); then I apply textures at runtime to pixels that have a certain colour.

Is there a fast way to have Unity process the colour material information of an object and apply a texture to it at runtime? And for when colours overlap a way to have the textures cleanly blend together to form a transition texture?