There are three basic approaches to choosing grout color:
1) Matching: By matching the grout and tile color, the grout lines become less pronounced and the tile itself is accentuated.
2) Contrasting: By contrasting the tile and grout colors, you draw attention to the pattern and layout of the tile overall. This may be the best choice with detailed geometric or decorative patterns. These days we see a lot of white subway tile with darker grout. Some people love this contrasting, bold and historic look (and appreciate that darker grout is effective at hiding dirt). Others think the grout just looks “dirty” from the get go.
3) Neutral: Opting for light neutral colored grouts in gray, beige and brown is probably the safest bet in many bathrooms.
There are pros and cons to both ends of the spectrum. Darker grouts hide dirt and stains but are also more prone to fading and staining from harsh cleaners. Lighter grouts, on the other hand, are more likely to show dirt. Some experts recommend shades that are neither dark nor super light. Colors like tan, beige, light brown and grey are easier to keep clean and less prone to fading and discoloration.