We were slow to realize that our second child was sensitive to food dye. I didn't buy many colored foods, and we made most of our own desserts.
Then my husband started buying flavored cream cheeses, first savory and then sweet. It was after strawberry cream cheese that our second daughter, then about 3 years old, went completely nuts in the car on the way to church. We had had a great morning so far, and suddenly she was screaming in the back seat that she hated her [favorite] dress and her [favorite] shoes. She was a wreck for about 20 minutes, and then her tears subsided and she was okay for the rest of the morning.
It was such a Jekyll-and-Hyde transformation, after such nice start to the day, that it got our attention, and we checked the label on the cream cheese when we came home. Sure enough, that light pink color that seemed plausible for strawberries actually came from food coloring.
We started reading labels, but sometimes got lazy when nothing had happened for a while. One day, a couple years later, we went through a drive through and she got an ice cream sundae with a cherry on top. Before I could pluck it off, she had eaten the cherry, and then she quickly finished the ice cream. By the time we got home she had a rash on parts of her body and was complaining about how much she itched. When I looked up the ice cream ingredients for that chain, not only the cherry but even the soft serve had food dye. This is common to get just the right shade of warm white that people expect, and if I'd been better prepared it wouldn't have come as a surprise.
After that we checked all ice cream labels, and mostly ended up buying Breyer's (just like my family had when I was a kid) because it has the shortest ingredient list in addition to no dyes. We watched for dye at parties and swapped for dye-free candy at Halloween. Our daughter knew to ask and avoid, and we tried to make it not burdensome. She would occasionally eat candy with dye at a party and come home with a splitting headache, or seem ok in the evening (tired and spacey not not cranky) and wake up with a splitting headache. It was like a hangover, and I attributed it partly to exhaustion and dehydration after exciting social events, not just the dye and sugar. We talked about drinking more water and pacing herself better.
When she was about 9, Winco came to town, and we bought some steak and mushrooms for dinner. When we arrived home late and made a quick dinner, I didn't register that the steaks in the package seemed red from the outside, but showed some brown on the inside when I removed them. We had a nice dinner and went to bed, and in the morning she had a splitting headache and threw up for several hours. She didn't have a fever and didn't seem sick otherwise, but sometimes the fever comes later, so I waited. By noon the headache and nausea had worn off and she was playing around the house. No fever. I thought back to dinner and realized that the steaks must have been sprayed with food dye, and I had been too preoccupied with putting dinner on the table to really think about what I saw.
Once I put it all together, we decided we wouldn't be buying steaks from Winco, and added another item for vigilance. A few weeks later, she visited a friend for the evening, and ate dinner there. The next morning she had the headache and threw up again. This family knew she shouldn't have food dye, and she knew, so I asked what they had for dinner in case there was something else I should know about.
"Just ground beef tacos," the mom said "was there a problem?"
I explained what had happened and how it was like the other time we bought beef from Winco, so it seemed to be related. It was good for the other family to know because she was sorting out her own health challenges. Winco does have a section of higher-grade meat, which is what we buy now if we shop there.
I felt lucky in a way that she had such uncomfortable reactions that even a strong-willed kid would be willing to watch it. Now that she's 12, and has a larger body, and drinks more water, a bit of food dye doesn't wreck her day. She takes vitamins and can manage her mood better even if she does feel a little gross. We still don't buy anything with dye, of course, and she avoids it when she's out, but she hasn't had a rash or headache in several years. We're lucky she's more resilient now, and fairly responsible.