Researchers have found that most people lose their appetite when served food dyed blue, because many blue plants and fruits in nature are poisonous. ================================================================= Extracted from my grammar book. I wonder if my grammar book has made an error regarding the unintentional omission of 'is' in front of dyed. I don't really think we can speak 'when served food dyed blue'. Instead, it should be 'when served food is dyed blue' Can anyone confirm it?