What is the background color of an opal?

An opal's bodycolor, independent of its play-of-color, refers to the primary color that is perceived in the stone when it is viewed in white light. This bodycolor can range from completely colorless to a variety of shades, including white, gray, yellow, red, blue, and black, depending on the specific opal type.

Understanding bodycolor is fundamental in colored stones, as it significantly affects the overall appearance and value of the opal. This bodycolor serves as a backdrop for the play-of-color, which are the iridescent flashes that can occur when the opal is moved or viewed from different angles. Recognizing that the bodycolor stands separately from the play-of-color helps establish a clearer grading system and appreciation of opals in the field of gemology.

The other choices do not accurately define the term "background color" as it relates to opals. On the contrary, options related to outer layers, synthetic coloring, and the bright flashes seen in opals pertain to different aspects of the stone and do not encompass the concept of bodycolor itself.