How to differentiate vertices with a weight of zero in the active vertex group and vertices which are not referenced in the active vertex group?

Question

I have already set the Zero Weights option to Active (Viewport Overlays > Zero Weights > Active) so that vertices which have a weight of zero in the active vertex group and vertices which are not referenced in the active vertex group are displayed in black.

But they both appear as black, and I would like to see the difference between the two, here's why:

Let's say we have 2 vertex groups. If Auto Normalize is activated, and I remove weight from vertices in the first vertex group, weight will be added to the same vertices in the other vertex group, but only for vertices which are refferenced in both of the vertex groups. And I can't find any way to visualy display the difference.

Here's an example :

We have a surface and two bones. The vertices of the surface have a weight of zero or are not referenced in the vertex group 1 (vertex group of the top bone). And the vertices of the surface have a weight of 1 in the vertex group 2 (vertex group of the bottom bone).

Then, with the vertex group 2 selected, I apply a weight of 0.75 with a strength of 1 on all the surface, with Auto Normalize activated. And so we see that only the right part of the surface is affected because indeed only the vertices of the right of the surface were referenced in the vertex group 1. And only thoses vertices have now a weight of 0.25 in the vertex group 1. And it would be practical to be able to visually distinguish it before the operation, because both were black.

So is there a way to differentiate vertices with a weight paint of zero in the active vertex group, and vertices which are not referenced in the active vertex group ?

Answer 1

If you'd like to know which vertices are assigned to a group, potentially even at 0 strength, you can switch to vertex masking and select the group from the properties viewport:

Even though they are black, the vertices at the crown of the head get selected, because they are assigned to the group. The vertices at the chin do not get selected, because they are not assigned.

I prefer enabling vertex masking whenever I weight paint, even when I'm just painting everything-- I need to know where the actual weights are, not what's interpolated across a face.

I have to add that using autonormalize on vertices with weights that are not yet normalized doesn't make a lot of sense. If you'd like to paint with autonormalization on an unweighted mesh, I recommend starting out by assigning all vertices at strength 1.0 to a root-ish bone and working your way out. (But I do not myself use autonormalization, mostly because it doesn't work with painting gradients, and gradients improve quality and save time dramatically; but also because with more than 2 groups on a vertex, I need to control exactly how normalization occurs, more carefully than autonormalize is capable of.)