Depends on the specific sign which you failed to list.
(in the US) White with black letter/numerals.
manditory instruction signs
Red and white.
Regulate
Those signs are called prohibition signs, and whatever is pictured behind the crossed out red circle is forbidden. Some examples: safetysignsservice.com.au/signs/prohibition-signs
Stop signs are red because it is a color that is easily noticed and associated with danger. White printer paper appears white because it reflects all wavelengths of light, making it appear white to the human eye.
Red, Yellow, Green, Orange, & White.
Gas signs on highways are usually red, blue, and white. Red is often used for prices and text, blue for background or borders, and white for contrast or accents. These colors are chosen for their visibility and ability to catch the attention of drivers.
They are signs of white supremacy
blue = loyalty red = bravery white = courage
Signs which denote Interstate Highways are red, white, and blue.