"Iso Yellow is short for Isoindoline which is itself a shortening of the full chemical name for this pigment. It is a vat pigment. Vat pigments are called that because they are made in vats but while that sounds fairly ordinary, vat pigments have a reputation for being particularly lightfast colors with all round good qualities. They have high tinting strength and are very clean colors.
Despite being simply called a yellow this particular yellow is a very reddish-yellow and is on the verge of being an orange, reminiscent of saffron robes on buddhist monks. Mixed with a red it will produce a brilliant scarlet, while used with a cooler yellow can produce the full range of yellows found in nature. Added to Burnt Sienna it can make the beautiful earthy colors seen in deserts.