They're actually talking about a very specific implementation of a dual-LED flash, where one LED is white and the other is amber in color. By adjusting the brightness and / or timing of each LED separately, they can produce a flash that is pure white, pure amber, or something in-between.
Professional photographers have used tinted flashes (by using gels, tapes and other color filters on their flash equipment) for a long time. What Apple claims is that this is the first time it's been done on a smartphone by using two LEDs of a different color.