a coloring agent added to pigments, dyes, etc. to produce any of a variety of fluorescent colors
adjective
designating, of, or like such a color or colors
See Day-Glo in American Heritage Dictionary 4
(dāˈglōˌ)
A trademark used for fluorescent coloring agents and materials. This trademark sometimes occurs in print in lowercase: “The troupe's staging . . . follows Alice's fantasy romp through day-glo daisies, past a smiling Cheshire cat”(Los Angeles Times).