Final answer:
The background color for warning signs, aside from construction and maintenance, and some school signs is Yellow, chosen for its high visibility and attention-grabbing qualities.
Step-by-step explanation:
The color used as the background color for warning signs (except construction and maintenance signs), and some school signs is Yellow. This color is one of the three primary colors—red, blue, and yellow—and it is known for its high visibility which makes it suitable for such signs that require attention and caution. The choice of yellow for warning signs is not arbitrary; it is based on the color's ability to stand out in various light conditions, thereby helping to ensure safety.