Tetrachromats are not seeing four well-separated colors. They are seeing the exact same blue-area and green-area colorrs, with two different cones responding slightly differently to red-area light.
So, instead of a color looking RGB(200,100,100) to them, it might look (200.26,100,100).
The very slight difference is why it's so hard to detect in people, and frankly, doesn't affect much (which is why there's apparently very little evolutionary "pressure" on the color genes).
Tetrachromats are not seeing four well-separated colors. They are seeing the exact same blue-area and green-area colorrs, with two different cones responding slightly differently to red-area light.
So, instead of a color looking RGB(200,100,100) to them, it might look (200.26,100,100).
The very slight difference is why it's so hard to detect in people, and frankly, doesn't affect much (which is why there's apparently very little evolutionary "pressure" on the color genes).