It doesn't matter what the original looks like. You can do whatever you want on top. If you paint over that, or blur it, or do Levels or whatever, then collapse the stack... the result becomes the new "original". After you kill the modifier it's just one set of color data.
That's weird, it works for me. Maybe you have the original color in another map channel? If you go to Tools > Channel Info, do you only have a single vertex color channel, and is it 0:vc ? When you add the Vertex Paint modifier, is it set to Vertex Color?
What exactly are you trying to do with the old colors? I can use the blur brush, use the Adjust Color dialog (HSV, levels, etc.). Erasing does show me the original colors, but TBH that's what I want to happen. If I want to kill the old colors completely in one area, I just paint over top. What specifically are you trying…
Wait... you can't cover the original with new vertex color? It's kind of like Photoshop's Background layer, if Photoshop prevented you from editing the Background. You can duplicate it as a new layer (Condense To Single Layer button), and do blurs and Levels on that. This completely covers the old Background/original. You…
Yep, if you want to Eraser paint bucket fill you can do several things: You can clear the channel Check on "ignore underlying color" Add a new layer and fill it with color then collapse? So there are some options there. I could see it being sort of problematic if you are using more than 2 colors, like if you are trying to…