from Harold McGee's "On Food and Cooking: The Science and Lore of the Kitchen":
"There's a useful guideline for estimating the relative healthfulness of vegetables and fruits: the deeper its color, the more healthful the food is likely to be."
This after a long discussion of the usefulness of antioxidants, a field of study McGee acknowledges is in its infancy. So if Poliquin is wrong, he's in very good company. And if you can really prove them both wrong, you should be writing your own authoritative books, not hanging out on this website.
As for ORAC, it's a speculative measure that is also in its infancy. Oddly, despite your assertion, onions are not on the Wikipedia page on the subject.
http://en.wikipedia.org/wiki/Oxygen_Radical_Absorbance_Capacity
And in any case, your point is ridiculous: no one considers onions a substitute for berries. They DO consider questions like "if I'm going to eat berries, which are healthiest?" or "if I'm going to eat a salad, which lettuces or greens are healthiest?"
Color IS a helpful guide for those questions, and to say otherwise is to blow smoke up our collective rear end and confuse people to the point that some will say "aw screw it, who needs fruits & veggies anyway?"