I would not use the word "need." We don't "need" the drinks to begin with, which is the crux of why they have dye in them. Several things, pretty colors of the right type make people like things more. Red and yellow colors make you hungry. Blue colors make you calmer and more serene. The artificial colors are there to make the products more appealing. We have found that some dyes do seem to be corollated with health issues, and the ones that appear to have a causal link have been removed and outlawed. There is a little more to unpack. Corrolated does not necessarily mean causal. For example, it is true that regular drinkers of diet sodas suffer heart attacks at a statistically significant higher rate than people that just chug regular, sugary soda, but the corrolation is not causal. The reason for the corrolation is that more heavy people drink diet sodas. The risk factors are already there. The diet soda is just along for the ride. As long as it is legal to do so, and adding color to things makes them sell better, people will continue to add the glitz.