Garlicgingeronion paste turning green

I was trying to make the chicken korma recipe out of Julie Sahni's Clbuttic Indian Cooking for dinner tonight. It begins with sauteeing a mixture of 3 cups finely chopped onion, 1 1-2 Tbsp. minced garlic, and 1 (okay, I used more than that) cloved minced garlic. I used canola oil, and a nonstick pan. The cooking utensil was one of those OXO nylon ones. I used a regular carbon steel knife to chop the onions-garlic-ginger, but further pureed it in a food processor to get a smoother consistency.

And the mixture turned GREEN. Pale green at first, but getting darker toward pea green as it continued to cook. This has happened once before, and I have no idea why.

I dumped out the first batch, then started again using only garlic and onion. Again, it started turning green. I decided not to continue because the last time it did this and I finished the recipe it tasted...off. No point in completing the dish when it won't taste right, but now I'm out of onions and can't make a third attempt until I buy some more.

Anyone have any ideas for why this happens and what I can do to prevent it again? Ruining dinner is one of the surest ways to put me in a foul mood.

Ariane