A radial gradient colors each point in space based on its position relative to two control circles. The color of each point between the two control circles is a linear interpolation between the colors of the two control circles. Points that are not between the two control circles, but that are inside the tube or cone formed by the two circles, are colored either completely transparent (if the nearest control circle is not extended) or the same color as the nearest control circle (if the nearest control circle is extended). Points that are not in the tube or cone formed by the two circles are completely transparent. A radial gradient can sometimes give the appearance of a sphere, tube, or cone.