What is the yellow-green dye-type solution that people spray on their lawn in winter and what is it used for?

The dye is helpful to the individual who is hydro seeding as it visualizes the area covered allowing proper application.

Just a a flamingo needs shrimp to get its pink color, http://www.chemistry.org/portal/a/c/s/1/feature_ent.html?id=c373e9fb622ebb078f6a4fd8fe800100 And a baby can become orange with too much carrot http://www.gardenandhearth.com/Baby-Food-Recipes/Preventing-Any-Surprises.htm grass can be made to look green when feed green dye. http://www.turboturf.com/Dye_Crystals.htm http://www.madsci.org/posts/archives/2002-04/1017816304.Bt.r.html also you can paint the blades http://www.topix.net/content/cj/18212755313465505054 this dye is also a addition to hydro-seeding http://en.wikipedia.org/wiki/Hydroseeding It also protects the seeds from bird consumption.