As the title says and the repair I am talking about is a crack due the building shifting. I am guessing a resin like stucco colour coded in as much as possible. I have the impression that ultimately its not possible to make a truly invisible repair but that's not what I am after, just a stable repair and here's the clincher - If the crack is relatively wide say 5mm+ is it worth putting marble chips in and grinding them down - if so where do get em or is as easy just smash a tile up?