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.  [![enter image description here][1]][1]The color is freaky.  Why did this happen?


  [1]: https://i.sstatic.net/3Qc17.jpg