Food coloring is far from "safe". Yes sure quite a few vendors (Makers of Pluid, and Tasty Vapor. + Others) Color their juice as a marketing scheme.
Here is an article I found while searching for food coloring side effects
Artificial Food Coloring Health Effects - Food Dyes and Additives - The Daily Green
I quote from the above article..
Still, the high-profile review by the FDA is focusing attention on the issue. So let's look at the Center for Science in the Public Interest's main arguments, set out in a 2010 report, Food Dyes: A Rainbow of Risks:
Cancer: Citrus Red 2, Red 3, Red 40, Yellow 5, Yellow 6, Blue 1, Blue 2 and Green 3, — which include some of the most commonly used synthetic food dyes — have been identified as being, or being contaminated with, potential cancer-causing chemicals. The potential carcinogenity is largely based on small-scale animal testing in laboratories.
Allergies: Blue 1, Red 40, Yellow 5, and Yellow 6 are known to trigger reactions in those with allergies.
Hyperactivity: In 2009, Britain asked food companies to phase out the use of most food dyes in children's food over concerns some studies had raised about their link to hyperactivity, attention deficit disorder and related health issues. (Other experts in the field have questioned the results of those studies.)
Of course that is eating food dyes. We don't know the effect of inhaling them.
Still, food dyes are GRAS - Generally Regarded as Safe. But at one time Cigerettes were considered safe. DDT, GMO, Agent Orange, etc.
BTW The vapor does not change color. Vapor is white because of the light going through the vapor molecules.