The best grout colour for white porcelain slabs depends on the look you want. Light grey or beige grout creates a soft, natural contrast while helping to hide dirt. If you want a seamless look, off-white grout blends well with the slabs but may require more cleaning. Darker grey or anthracite grout can add definition and make the slabs stand out more. It also hides stains better, making it a practical choice for high-traffic areas.