As you know, ordinary white light (for example, solar) can be decomposed into a color spectrum, separating electromagnetic waves of different lengths from each other. This can be done with a glass prism, just like in school experiments. The resulting spectrum consists of red, orange, yellow, green, blue, blue, and violet smoothly turning into each other.
And now we turn this spectrum into a ring, connecting purple and red ends and placing a purple color between them. Get the same color wheel. The Swiss artist Johannes Itten placed 3 colors in the center of the circle: yellow, blue and red, from the mixture of colors of these colors all the rest are obtained.
The mutual arrangement of colors in the circle and gives us a huge variety of design options for anything. How does this happen? There are different ways to "choose" colors from the spectrum, and they are all tied to their location. For example, a monochrome scheme allows you to select several shades of the same color.
The contrast scheme is a combination of two colors from the opposite parts of a circle.
Multiple scheme tells you combinations of several colors, located at equal distance from each other - they will also be well combined with each other.
There are online services that allow you to select colors. For example, this one. Try to play with them, creating different color schemes - to understand the principle and master the tool, you need only a couple of minutes. Familiarity with the color wheel will allow you to understand the causes of various design decisions and, possibly, come up with your own ideas.