Food coloring! I will just say this. I use them to hide what I have put into baits. That the main reason I think that they are use. I have seen fish hit different colors better at day and night, but at the same time be hitting the other hope that make scents to you. I like red (day time), green (night time), black (anytime) and yellow (anytime). Blue I have not had any luck with much at all over the years. Really it seems to hurt the bait for me. If I use something that gives it a blue color say as a flavoring I will use something to change it to something else the color that is. Well comes to mind blue I did have luck with a work shirt button as a pick up on the hook. We use them for years on the hook have caught fish on just them too.
Other things! Baby food, so many kinds used them a lot over the years. The ones I like are carrots, squash and banana. They are just the ones that I use the most over the years. Whit these you can have about anything that you want to try. Be sure to look at the different kinds of cereal, like grits, rice, cornmeal, wheat gram and oatmeal fish foods. You can even get stuff to put in a bridler like noodles, chow, millet, wheat bran, wheat, it self and a lot of other seeds and stuff. Be sure to check them out at the store the next time that you are there with the wife. You will see things that you hadn't thought of before once that you start to look for it. Oh check out the Kool-Aid, jelly, Jell-O and the juice section you will see a lot of things. Another good place to look at is health food stores.
Don't forget things like Ketchup, tomato sauce and puree. Then you have the corn reg and cream. Also pie filling. They are good to use sometimes in good pack bait. I bet that they would be good in them there oats that they use today. That would help from them drying out so much you know what I'm saying. Even some ketchup I believe would do that. Don't forget to stop by the spice rack while that you are looking around. I think that is enough to give you the idea of it all and what to look for. So I will stop with this for now.