Need help with vertex paint layer material

Currently I’m trying to recreate landscape material from The Last of Us Part 1 with all features like puddles, snow clumps etc.

I made material with multiple layers for each channel and it look like this

  1. Base Layer - Soil
  2. R - Grass
  3. G - Snow
  4. B - Puddle

But I have a problem with next step - adding melted snow around my snow layer like here

Is there any solution to achieve this kind of effect? What nodes could I use? Maybe isolate somehow snow layer borders?

Will appreciate any kind of help - links, tutorials, etc. Thanks!