Color is an infinite-dimensional space since you can have any amount of any frequency EM waves. Humans eyes reduce that infinite dimensional space to 3 dimensions, centered on RGB.
Or to be more precise, for them instead of equal proportions of 560 nm/530 nm/420 nm light being white, their own white might be something completely different like 550 nm/460 nm depending on their photoreceptors. Which would absolutely not look white to us. And mantis schrimps would need equal proportions of 16 different wavelenghts to see what they could call white.