My guess is that the orange stains are due to storage of the quilt on unsealed wood, either on a shelf or in a drawer. The other main cause of orange discoloration to fabric, hard water stains, would be pretty much all over the quilt, not in "color blocks". The green stains are more of a puzzle, but could be anything from mold to fabric softener.
As far as antimony is concerned, it is the reason I no longer buy bottled water. Also from Wikipedia: "Antimony and many of its compounds are toxic. Clinically, antimony poisoning is very similar to arsenic poisoning. In small doses, antimony causes headache, dizziness, and depression. Larger doses cause violent and frequent vomiting, and will lead to death in a few days....Antimony leaches from polyethylene terephthalate (PET) bottles into bottled water, but at levels below drinking water guidelines."