I boiled sliced yellow squash with ravioli, and it turned bluish-green -- why? Boiled cheese ravioli for 10 minutes.  Added sliced yellow squash for the last 3 minutes.  Nothing else in the pot but boiling water, not even salt.  It looked fine cooking but after I drained everything in the colander, the squash rind stayed yellow but the flesh turned bluish-green on most pieces.  Not all pieces though.  It tastes the same as usual.  The color is freaky.  Why did this happen?
Probably the same reason why garlic turns blue sometimes when you cook it.
http://www.foodsafetysite.com/consumers/faq/?m_knowledgebase_article=14

its a reaction with sulfur + copper which can naturally occur in foods.