From my knowledge Nippon has a system which lets you paint a sort of primer over existing tiles, then two layers of paint to finish. Bear in mind that any texture/structure or existing cracks or imperfection due to wear and tear, even the minor ones, will still be visible even after you painted it. But you have the freedom to mix the paint colour you want. Since this is a system, and usually warranty comes with them, it is more advisable to get them to supply and install, otherwise if you decided to apply it yourself, the warranty may be void.