A grade in GIA’s Color Grading System…. at the end of the “Light Yellow” category.
Yttrium Aluminium Garnet, used as a somewhat unconvincing diamond simulant before Cubic Zirconia.
Most diamonds contain nitrogen which gives them a slight yellow, “touch of warmth”.
The usual diamond bearing rock in which diamonds are found is called Kimberlite or blue ground. As this rock is exposed to sunlight and the weather elements is begins to decompose and its color changes from blue to yellow. This yellow ground is easier to break apart in the search for diamond rough.