How to make background/text color generator?

Question

PHP

Two questions are of interest:
1. How to make a complete opposite or spectrum of opposites with respect to the first color (so that, for example, the background and text (black and white) are clearly distinguished). Colors in the formats #ffffff and #000000 ? Ideally, three colors (text, background, frame)
2. How to implement this in php or maybe there is some mathematical formula?

Answer 1

here is a php library there is a complementary() method it returns the opposite color mexitek.github.io/phpColors