So what you're saying is that black actually isn't a color. It's the absence of color. Or is that white? Or both?
Look up additive color
and subtractive color
. Because they are different. In additive color (what you see on a screen) when red, green, and blue light are combined, the result is white. It takes only those three colors to create all others.
In subtractive color (what is applied to a surface with ink, dyes, etc.) when cyan, yellow, and magenta are combined, the result is black. It takes only those three colors to create all others.