Many things we consider white, aren't actually white.
For the purposes of the RGB color model that is used in digital photography, white is - Red=255, Green=255, Blue=255.
R=255, G=240, B=255 isn't white. R=250, G=250,B=250 isn't white either. But, when the RGB values are all the same wew have a tone of neutral gray.
In the RGB model black is R=0, G=0, B=0.
Sunlight is actually a yellowish tone, and isn't white.
Most flash units fairly closely approximate sunlight