To expand on Adam's response, I'll bet that it's a fresnel shader placed in the material's "Color" channel. Since each face seems to change color quickly as it moves, I'd also guess that the gradient he used in that fresnel was pretty tight, i.e. very little fade/transition from color to color across the gradient.
ok cool that seems to make sense. could you tell me how the object was made? it looks abit like a platonic shape with the points moving around. have had a go trying to randomise the point location but not really getting anywhere! or is it keyframed?