Polybrush Vertex Painter changing colour

Been trying to paint some (probuilder) terrain with the vertex painter in Polybrush, but each time I release my click, the colour is changed to something else.

After further experimentation, it seems to essentially be choosing the opposite colour to whatever currently is being hovered over on the terrain.

https://imgur.com/a/6IOJNVz

I currently have black selected, but it's not allowing me to paint with black. The colour of the brush changes as I move my cursor over the different colours of the terrain. The reason why it's so colourful is because I've been trying to paint it for ages and the colour keeps changing to something new.

Also, when I create a new object and attach a brand new Polybrush/Diffuse Vertex Color shader to it, it starts off with a yellowy-brown tinge, as opposed to being completely white, like i've seen in heaps of videos.

I just want some green terrain

 

I fixed the problem.

Having the strength of the brush higher than 1 seems to create distortion in the colour.
If the brush is set to 1, the correct colour is painted.