Attached Link: Visit the Node Cult at RDNA

This is very easy. If you want to keep using the Toon node for the black lines you can, or you can just skip the toon node.

In any case, plug Diffuse into a Math_function:Floor node. Floor rounds down to the nearest integer. Since Diffuse produces values between 0 and up to 1 generally, taking 4 times that produces a value from 0 up to 4, and then Floor of that rounds it down so you get exactly 0, 1, 2, 3. Then you plug .33 of that into a ColorRamp, and it becomes 0, .33, .66, or 1, thus selecting the exact colors in the parameters of the ColorRamp. No gradient will be produced. And that is all there is to toon shading.

Here at Rendo people like to say you need to buy stuff or it can't be done. You should ask such questions at RDNA - it's a can-do place.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)