Clear, or transparent, isn't considered a color. It is a different visual property altogether. The color of a physical object depends on the light that is reflected, absorbed or emitted by the object, while transparent matter lets light pass through it without reflecting or emitting light. Thus, it has no color.
When looking at a clear object, the object takes the color of whatever is behind it with respect to the viewer. Examples of transparent matter include glass, air and water. Objects that are semitransparent, or translucent, have a color of their own, as a significant portion of the light doesn't pass through and is reflected instead.