Hi, is it possible to blur or fade the edges of a vertex paint with nodes?
Vertex paint blurs automatically-- between each vertex, across each face.
If you want the blur looser than that, extending over more than a single face, you have to paint the gradient. There’s nothing you can do in nodes instead. (But you could data transfer vertex color, nearest face interpolated, from a lower poly object; and of course, you could use a texture instead.)
If you want the blur tighter than that, you can either create more loops, or run your vertex color through something like an RGB curves node to control the interpolation across faces.