Why is it best to serve food on white dishes?

Food was originally served on white plates because they were cheaper. That has been the case for many decades, though today china is available in many colours and designs at around the same cost, so you can have different colour plates to go with different colour foods.

Plates were originally round, again because they were easier to make and therefore cheaper. Now it's just as cheap to buy plates or bowls that are square, or other shapes, and they can look very effective on a dinner table.