I've found that certain figures have really intricate material layers, which makes removing them quite tedious. Is there a shortcut or something to make removing the textures a breeze? Also, is there a way to quickly change the diffuse color, and also use a preset pallet?

if it's the same figure every time then just strip it down and save that as an MC6 material preset.

You could make a single material, save that as an mt5, apply it to a single material zone, then select the option to 'Apply to all' (I can't remember if that's a wacro or in the right-click menu). Then save as mc6 collection as ghostship says.

Set up your node(s) on one material

select the nodes you want to copy

right click on one of the nodes

select "apply to all"

hold down Shift and click Remove detached nodes on the wacro panel

to change your diffuse colors quickly try this

# -*- coding: utf-8 -*- 
# ©copyright structure 2001 - 2020
# ================================

import poser
import wx
scene = poser.Scene()
materials = scene.CurrentFigure().Materials()

import wx.lib.agw.cubecolourdialog as CCD

#----------------------------------------------------------------------
def colorDialog():
    """
    This is mostly from the wxPython Demo!
    """
    dialog = wx.ColourDialog(None)
    
    # Ensure the full colour dialog is displayed, 
    # not the abbreviated version.
    dialog.GetColourData().SetChooseFull(True)
    if dialog.ShowModal() == wx.ID_OK:
        data = dialog.GetColourData()
        return (data.GetColour().Get())
        
    dialog.Destroy()

#----------------------------------------------------------------------
def RGBToPoserCol(rgb):return tuple([x/255.0 for x in rgb]) #courtesy of Snarlygribbly
#----------------------------------------------------------------------

r,g,b = RGBToPoserCol( colorDialog() )

for material in materials:
    tree = material.ShaderTree()
    nodes = tree.Nodes()
    for node in nodes:
        if node.IsRoot() and not node.Type() == "CyclesSurface":
            inputs = node.Inputs()
            i = inputs[0]
            i.SetColor( r, g, b )
            tree.UpdatePreview()

If you want instantly and automatically strip the materials from an entire figure, SnarbyGribby's free EZMat for Poser will do it.

"is there a way to quickly change the diffuse color, and also use a preset pallet?"

SnarlyGribbly’s free EZmat for Poser (linked above) has a "Randomizer" script in it. This randomises the diffuse colors, to give you a Clown Pass. Not quite what you want, but near.

It sounds like you want what Hollywood calls a "MATcap" - to have Poser automatically capture a material's average color, and then replace with the material with a simple diffuse using that averaged color. Such a thing would be useful for comics makers, and we can only hope to see a MATcap "insta-comic" button added to Poser 12's comics features. It would be even more useful if we could then apply a palette-shift to the results, so as to reduce the applied colours to stylized shades of gray (for instance).

Stripping materials, and then adjusting diffuse colors down to a limited pallete - that sounds like you are making comics with Poser.

If you are making comics, you should be Preview-rendering to separate inks and color layers. Then combining these renders as layers in Photoshop, first knocking the white out of the inks render and then dropping it on top of the color render.

Doing a comic this way lets you filter the colour render, without ruining your inks. You can do things like using a "Replace Color" Photoshop Action on the color render, or third-party simplification filters such as Topaz Clean. Again, this may approximate what you want to do.

That Clown Pass or Mat ID would also be extremely useful for making masks when compositing in an image editor - I didn't realise EZMat had that, it'll come in handy so thanks for pointing that out!

Now all I need is some way to do a ZDepth pass in Superfly and I'll be happy ;)