What is Day-Glo?

Day-Glo is a type of flourescent paint that appears to glow brightly in the sunlight.  It was used as a high visibility paint on various rescue aircraft in the 1950's and 60's.  The ultra violet rays from the sun causes the pigment to glow, much like some pigments under a black light.

"Day Glo" refers to fluorescent colours (it's actually a trade-mark, which has fallen to common use). In your case, with reference to a CG helo, I am assuming that the colour you are looking for is a fluorescent red-orange (FS  28913) or fluorescent red (FS 28915)

The only fluorescent colours in the Tamiya range are those for their Mini-4WD range, and are only available in spray cans or marker pens.

Alternatively, fluorescent orange is available from Testors (1367A), Model Master II (2041) or Gunze (GSI Creos) (H98), or for fluorescent red, Gunze (H99), Model Master (1775 )