We document an exceptionally large, 25.85 ct diamond that shows a slight colour change but exhibits some atypical properties for chameleon diamonds, including white luminescence to long- and short-wave UV radiation, as well as a network-like pattern seen in most orientations with the DiamondView. In considering whether to call this a chameleon diamond, we undertook a review of available data to compile the properties that are commonly exhibited by these gems. We found that, in addition to their defining photochromic and thermochromic behaviour, nine characteristics all must be present: long-lasting yellow phosphorescence, a zoned DiamondView growth pattern showing yellow-green/blue/inert areas, the presence of dominant A aggregates and also some hydrogen in the infrared spectrum, a continuum of absorption in the visible range related to a very weak type Ib character, a 480 nm absorption band that is possibly related to trace amounts of oxygen, a 425 nm absorption band, a weaker absorption band in the red to near-infrared region consistent with hydrogen-related defects, and traces of nickel detected with photoluminescence spectroscopy.