The recipe, which I scissored out of the morning paper, includes the following words of counsel:
The peas are added at the last minute, which help maintain their vibrant green color.This is one of those infractions that becomes more obvious when you say the sentence out loud. It's not the peas that are helping to maintain their color, it's the action of adding at the last minute, so we don't need the plural verb. It should be "helps." I would also point out that almost any time you put a color next to the word "color," one or the other can probably go. Since we all expect peas to be green, we can simply say "their vibrant color" in this context.
And what vibrant color, indeed! As proof, I offer this un-doctored photo of last night's repast:
Note that for optimum vibrancy, one must also blanche the peas before introducing them to the mixture.