The question is really what colors of tile SHOW dirt the most. A black tile may visually display a lot of dirt but might actually be less dirty than a multi-color tile that is simply doing a better job of hiding the dirt. There is also the very subjective question of what is filthy to one pair of eyes is acceptable to another pair. Generally speaking, shaded, light colors will be easier to clean than stark dark values. However, there is no hard and fast rule.