We are only using the red channel at this point to paint vertices. To add an additional channel (say to add a dirt layer on top and change colors_ we would use an additional Lerp that uses the next channel available.
Use the BreakOutFloat3Components to separate each channel and input it into the correct material output (e.g., red channel lerp goes to Metallic, green channel to Roughness, blue channel to Ambient Occlusion). Please note that these channels as set up here are driven only by the vertex color being painted in the red channel, and not the others which remain available for use.
The alpha channel of HeightLerp is Transition Phase (S) instead of the Lerp node's Alpha.
HeightLerp varies the transition between the two textures with the input of a third given texture. The Height Map can be any texture. White are the first parts to use the second input and darker parts will use it later. Using a Scalar Parameter, we can control the contrast of the transition.
The disadvantage of using a static switch (boolean) is that it generates two versions of the shader, becoming more expensive in performance.