The purpose of this discussion is to raise your awareness of the laws that govern what we can add to foods. In particular, you should pay attention to the criteria set for determining safety and compare criteria set for pesticides vs added substances vs substances that are not added. A quick look at definitions from the FDC Act should be useful. Would you have defined food this way? Food additives may be defined by what they are not. What would this definition include?
The Adulterated Foods portion of the Act provides much of FDA's power. Read this carefully. How are added and not added substances treated differently? The Act also demonstrates Congress's understanding of the need for tolerances for necessary ingredients and sets some criteria for safety.
You should also be familiar with the Delaney Clause. The Food, Drug and Cosmetic Act is a law passed by Congress and it gives FDA the authority to do a number of things. Implementation of this authority is done through regulations. FDA's regulations can be found in Title 21 of the Code of Federal Regulations. You need to be very familar with the parts of Title 21 that deal with food ingredients. In particular, colors are found in Part 70-74., food additives are found in Parts 170-174 and GRAS substances are found in Parts 180-184.
Substantial information on the regulatory process can be obtained webpage of the Food Additives and Premarket Approval section of CSFAN. In particular, you should scan Code of Federal Regulation (CFR) Sections and Guidance Documents for Food Additive and GRAS Affirmation Petitions. Be sure to read sections: 170.20, 170.22, 170.30, 170.38, 171.1.