What is the background color of semi-black opal?

Semi-black opal is characterized by a background color that is typically grayish. This opal type exhibits a dark body tone, but not as intensely dark as black opal. The grayish hue allows for the play of color, which is a defining feature of opals. Semi-black opals can display a beautiful spectrum of colors against this background, often appearing more vibrant due to the contrast. Understanding the color characteristics helps in identifying and valuing opals correctly.

In contrast, black opal will have a significantly darker tone, while yellowish or brown background tones would categorize the opal differently, thus not fitting the specific classification of semi-black opal.