I want to create a node to use for probability masking like the node in the screenshot. It's a technique used for creating realistic fur textures. Do I use an attribwrangle node? https://www.youtube.com/watch?v=OuHdgK5jOtQ [www.youtube.com]

Well, I don't have the time to show a multiple colors workflow but, when I use just a mask to go from red to blue, I'd use a wrangle with
(*I'm skiping some steps)

That way, if the mask is zero, it's red, if mask is one, it's blue but all values between zero and one will give either red or blue (not blending, just solid colors)

Do you know what the masks for green, white, and black are?

From the paint sop nodes she uses, I think it creates float mask named c1, c2, c3, c4 (white, green, blue and red).

I mean values.