While some colours work better than others under a black light, almost any colour can glow if a fluorescent is added or if it is naturally phosphorescent. A black light gives off concentrated ultraviolet light. You can't see this part of the spectrum. When the ultraviolet light is shone on a fluorescent or phosphorescent substance, the fluorescent absorbs the light and casts it back immediately, creating a longer wavelength of light, making it visible to the naked eye and causing it to glow.
White paper, paint and fabrics are treated with fluorescent additives to make them brighter. These compounds react to the ultraviolet of the black light, casting them back quickly which emits that glow. Washing powder whiteners make clothing a bit fluorescent. White toothpaste with tooth brighteners glows incredibly strong.
Bright yellow hues of paints and fabrics will glow, due to the additives to make them bright. You can buy yellow specifically in neon or fluorescent, which has extra additives for the brightness.
Greens that are dark do not glow. However, a lighter shade of green, again due to the fluorescent brighteners, will glow. Neon greens cast an eerie green light.
Orange glows under black ultraviolet light. Neons glow the most due to extra fluorescent additives. Reds do not glow, or barely glow an orange colour, even if fluorescents are added.
Bright purples, from deep violet to the lavender end of the spectrum glow, as they have a fluorescent tinge. The glow will be stronger if you add a fluorescent compound or a brightening compound.
The lighter the blue the more pronounced the glow. With a fabric, add a bit of whitener or brightener to emit more fluorescent glow.
Pink, hot pink in particular, has fluorescent lightwaves in its make-up, causing it to glow under a black light.
Certain clear or "invisible" substances will glow when an ultraviolet line is shone upon them. Fishing line has fluorescent particles which will emit. Jellyfish may look colourless, however some of their proteins are fluorescent and they will glow. Blood and other body fluid proteins also emit a fluorescent glow under a black light. Investigators use special ultraviolet lights in collecting evidence and solving crimes. Antifreeze is manufactured with fluorescent additives to assist law enforcement to reconstruct a crime scene.
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