I recently noticed I had an issue where no Maxis or custom recolours are showing up for any build mode items for M&G stuff in my game. Using the design tool merely says the item is non-designable. I've uninstalled and reinstalled CEP, what I first thought was the cause and done the same methods completely taking out my downloads folder so I'm not sure where the issue lies now.

Could they problem lie with the materials/catalog files, something like that from within my program files? I've done a few lighting and graphical tweaks over time but I believe I still had recolours during and after those modifications. Any help would be appreciated and I'm curious to know why the effect is only for objects with the particular pack as well because the Second Empire and Art Deco build sets I particularly enjoy using.

Those came shipped recolorable with recolors, so your SP9 files have either been edited or deleted. Either fix via Origin or resinstall that pack using your disks.

In regards to the CEP install - if you've completely taken out your Downloads folder, did you remove the "_EnableColorOptionsGMND" file? That one is a part of the CEP, and is needed for it to work. Make sure to keep it and a Downloads folder (if empty) in while testing.

Not sure if that's going to have anything to say for those windows, though. Probably something wrong with the install.

I repaired my game via the option on Origin and the recolours reappeared. All is now right.
Seems like an obvious suggestion come to think of it and did not expect such an easy fix. Thank you all heaps for the help!