Looking for a non-toxic, environmentally safe highly colored or intense dye I need a dye that is &quot;highly colored&quot; or intense.  I want to put it in water and flow the water in the form of a liquid sheet that is around 100 microns thick.  A number of spray nozzles use this principle to produce droplets.  The liquid is first formed into a sheet that breaks down after a few milliseconds into droplets.
The issue is that at such thin thicknesses, colors often disappear even if they look very intense in a tank.  I'll be working with around 0.2 gallon per minute to 0.5 gallon per minute flowrates, so something that hopefully can be added in relatively small quantities.  But more important is that the dye is non-toxic and environmentally safe.
Thanks for any suggestions.
Many organic dyes which are fluorescent can be carcinogenic like the famous Rhodamine dyes. You can try a couple of tricks. One of best inks, at least for demonstrations, is the yellow highlighter's ink which fluoresces bright green in water (see my photo below). If you can shine a bright white LED or a bright blue LED, it will fluoresce very strongly. You can use an optical filter in front of the camera that can block blue light and let the green and longer wavelengths in. With that you can increase the sensitivity.
Note that fluorescence intensity is directly proportional to the incident light intensity in dilute solutions.