The whole mixing colors is white is kinda misleading.
Colors only exist inside our mind, they don’t exist in physical reality. We have three receptors for wavelength information in the em spectrum in our eyes. They are S, M and L type and they are sensitive to a different range of wavelengths. The M and L range overlap quite a bit and are sensitive to a wider range of wavelengths. The S is apart on its own and quite focused. The receptors turn that wavelength information into signals our brains can read out. Simply speaking the eyes tell our brain for a given part of our retina we have x amount of S energy, x amount of M energy and x amount of L energy. That’s all the information we get.
So our brain combines this information and decides what color it’s supposed to be. As a child we learn what the different colors are. So we correlate those energy levels to the colors we are taught. This is highly subjective as each brain and set of eyes is different. Most men for example have less sensitivity to colors compared to most women (exceptions exist, this is generally speaking). Thus men see different energy levels, but still can see colors just fine for the most part. However women are on average able to distinguish between more shades of the same color, because they have more information to work with.
In the modern era however we found out our brains aren’t very picky and will just guess what color something is. In sunlight there is a broad range of wavelengths, which we associate with white light. However when making white leds we found out you can just output some spikes of light in the correct ranges and our brains will say jup that’s white. You can also output shit outside of the wavelength of our three detectors and we don’t notice or care. This makes cheap energy efficient white leds possible.
In the early days the peaks were very narrow with not the best wavelengths. We would see this light as white, but it wouldn’t be comfortable. Without saying exactly why, we would experience the light as harsh or get headaches after a while. Modern white leds are very comfortable for our eyes and available in a whole range of whites to suit our needs.
So while a whole lot of wavelengths combined like the light from the sun is white. A bunch of random spikes is also white. It doesn’t have to be all colors.
Also because colors only exist in our minds, things like grayscale colors, impossible colors and metallic colors are also a thing. There’s a whole lot more to colors than just em radiation at a certain wavelength.