Assertion: opal's background | /r/HasProperty | dark
Facets:
Source sentences:
text: Black opals (very rare and valuable) have a dark background and colours ranging from brilliant red through to greens, blues and purples.
text: Black Opal is distinguished from other opals by their dark background (Body Tone) and this characteristic enables the brightness of colour of which they are known.
text: Black Opal is distinguished from other opals by their dark background (Body Tone) and this characteristic enables the brightness of colour of which they are known.
text: However, it has become known that Boulder opals can also be described as black opals because of their dark background.