It is the shape and type of silver crystal that determines how light reflects back from it, and therefore what image tone it presents. And that shape and type determines how it reacts to toning.Why is it that a warmtone paper like Fomatone responds so aggressively to toning while Ilford Multigrade does not? Its all just silver by this point isn't it?
Ilford Multigrade neutral tone papers are designed to give extremely predictable and repeatable results under a wide variety of conditions. That means a very consistent image tone, but it also means relatively small response to toners.
The Ilford Warmtone Multigrade and Cooltone Multigrade papers are much more responsive to toners. When un-toned, they are also more variable in their response to varying conditions.