Grape Juice Allergy?

palm513

Around 6ish months my twins started eating grape baby food and loved it so I mixed a little purple grape juice into their cereal and they started throwing up, they got cranky and then had diarrhea. So we never gave them any more purple grape juice, but we tried white and they were okay with it we also tried them on the grape baby food again and they tolerated it fine. 

Yesterday, we decided to try them on grape juice again just incase they were to young to process it before and the same thing happened(they are 14 months now) is it possible to only be allergic to the dark purple concord grapes and not any other color? Or do you think it is something else in the juice.

I am planning on talking to the doctor at their 15 month appointment.