Food coloring is a liquid dye. It will mix with whatever chyme it encounters in the stomach and small intestine, dyeing a large portion of the stool. It does not prove that food stayed in a single-file line.

Also, again the GI-tract as a whole is also not a "one-lane road".

Please educate yourself and do not do "experiments" on yourself. A good place to start learning more would be: https://accessmedicine.mhmedical.com/book.aspx?bookid=691 if you're intrested.