How the eye works:

Red, green and blue are the additive primary colors of the color spectrum. Combining balanced amounts of red, green and blue lights also produces pure white. By varying the amount of red, green and blue light, all of the colors in the visible spectrum can be produced.

The human eye has three types of cone cells,RGB we see all the colors with these 3 cone elements

Why do we build RGB fixtures and RGBWA fixtures

To get white it takes RGB to be full on, that requires 3x the amount of current or power for white

If I have a dedicated led for white it requires less power to product white.

That is the only reason for extra led colors. The disadvantage is that given the same size area of space we have to put smaller led elements for the extra colors. thus less brightness per color led chip. It's a plus and minus game.

That's why there is still RGB only fixtures in the marketplace

FYI: About 8% of men and 1% of women have some form of color impairment.

The eye's electrical signals travel from the retina through the optic nerve to the brain.
Then the brain turns the signals into the images you see.
When light hits the retina (a light-sensitive layer of tissue at the back of the eye), special cells called
photo receptors turn the light into electrical signals. These electrical signals travel from the retina through
the optic nerve to the brain. Then the brain turns the signals into the images you see.

The eye has a logarithmic response to light, this means that for you to perceive light to be twice as bright,
it takes 4 times more light output of the light to double the brightness to the eye.