This is very true, cobaltDream. It seems odd to me that plugging simpleColor() into the Diffuse_Color channel doesn't produce a colour change in preview, whilst plugging an imageMap into same channel does. Doesn't make sense to me, but then, I'm quite certain I'm not in possession of all the facts surrounding that Diffuse_Color channel.

Not to further hijack the thread - I do keep doing this! Sorry! - here's the shader for the teeth:

...and thank you for confirming what I've discovered... I'm sure if I had read a bit more (so MUCH to read on here! by BB) I would have picked that up.
One more reason why I feel so strongly this forum isn't the best way to get the message across... those that know keep repeating themselves even to those who have searched.

Monterey/Mint21.x/Win10 - Blender3.x - PP11.3(cm) - Musescore3.6.2

Wir sind gewohnt, daß die Menschen verhöhnen was sie nicht verstehen
[it is clear that humans have contempt for that which they do not understand] 

Metaphor of Chooks