Removing placeholder textures

When im creating a structure I usually use placeholder textures to flesh out the building while im making it and I usually replace the textures afterwards with decent quality ones I make/photgraph. The thing is the placeholder textures are still aplied to certain hidden faces. I tried using the select same material option to switch them but it didnt seem to get all of them.

I wouldnt mind all this but it seems to be causing errors when Im trying to relight the building inside TGEA.

Anybody got any tips?