@spikeyxxx One question to your last image in your post here (with an orange frame): At the “MixRGB” node (set to “Add”) you put a label that the output vector still has “negative values”. But since it’s a “Color Output” socket, isn’t it clamped to the interval [0, 1]?
In the node setup screenshot that I’ve posted above, I think that the guy who has created this, maybe just by habit used the “Math” node instead of the “Vector” Math” node since the first one, at least to my perception, is more often used in tutorials than the second one (oh, a pun 😉!). With a “Vector Math” node, the “Separate XYZ” node would really just isolate the Z-component.
