24 Hours After Whitening, my Two Front Teeth Have Yellow Stains and Yellow Streaks. I Eat White Food Only?

I have completed 4 weeks of teeth whitening using take-home custom-made trays from my dentist. I used 10% and 16% carbamide ( mostly 10%, only used 16% for 5 days ). My teeth looked perfect. Just 10 hours later I noticed one small, faint stain on the bottom of one tooth.Next day , there were more stains ,3 days later , pretty much entire surface of two main front teeth was covered in yellowish stains and streaks.My dentist was puzzled .I ate white food only.