"Colored text" glow on signs at night

if you try to type on sign at night a text in any color (except black) you will see the text are glowing and you can see the text from far away (you can even light up a room XD )
tip: text glow can see even out a room (see the screenshots)
Other tip: gray text it's the most weakest glowing

samsung galaxy s4
4.4.2 (kitkat)