Adding more colors will mix up your brain by using illusion or seizures on it and it will become an issue if it happens, but showing different colors by only one is only the priority to it, because of that, the creator knows why you can't use more than one color by pixels because it will confuse your eyes and/or brain. Each pixel consists of three parts – subpixels – which each emits only one colour: red, green and blue. The resulting colour perception that our eye acquires is created due to a so-called additive mixing model of these three colours; this colour model is known by the abbreviation RGB. Example: LCD screen uses blue, green, and red, on old screen TVs.
When all three primary colors are combined at each pixel, this allows for as many as 2^8* 3 or 16,777,216 different colors, or "true color." This is referred to as 24 bits per pixel since each pixel is composed of three 8-bit color channels.
