The white fur with black-spots in the paintings of the 17th-century Dutch painter Vermeer is often considered to be ermine, which has been regarded 'royal fur, ' though he depicted ordinary citizens in his works. Why do the citizens wear royal fur? Is the fur really ermine? It cannot be concluded that Vermeer depicted the fur as ermine in view of reality or representation. The fur in Vermeer's paintings is probably modeled after more available kinds of white fur such as squirrel, rabbit and cat, to which he intentionally added black spots on canvas. This case confirms that even paintings that are considered realistic and meaningful may include fictional expression of costumes, which casts doubt on whether they truly reflect what the people of the time wore or the feelings they had about dress. We should be extremely careful not to treat such fictional expression as real and to put it properly into the context of the history of costume.