You are confused and I understand because even on this site, you can read phrases like "our eyes have cones for Red, Green and Blue light" and "Red light activates the Red cones".
- It is a common misconception that the receptors in our eyes are so, that the different types of cones correspond specifically just to Red, Green and Blue light. In reality, the three types of cones are sensitive for a range of Short, Mid and Long (depending on where they are positioned in the visible scale) wavelengths. It is very important to understand that they cover a range of wavelengths, and that they overlap.
Even if you wanted to put a arbitrary conventional color coding for these, you would have to put Yellow, Green and Blue instead of RGB. But these cones have a range of sensitivity, and multiple types of cones could be sensitive for the same wavelength photons. All along the visible wavelength range, there isn't a single position where only one type of cone would be sensitive, that is, every single wavelength photon would activate multiple types of cones.
- It is another misconception that whenever monochromatic light shines into our eyes, only one type of cone gets activated. In reality, whenever light shines on our eyes, may it be monochromatic or not, multiple types of cones get activated, it is just the level of activation that is different for different wavelength photons. Whenever monochromatic red light shines into our eyes, even if the photons would be all the same wavelength, they activate both the Long and Mid cones. The more the Long cone gets activated, the more reddish the shade is, the more the Mid range cone gets activated, the more Orange/Yellowish the shade is perceived by our brain.
Our brain is the one that perceives the colors as a combination of signals from the cones, and our brain is the one that perceives violet as a combination of signals from the Short and Long cones too. The more the Short cones get activated, the more violet the shade of the color is perceived by the brain, the more the Long cone gets activated, the more Bluish the shade is perceived by the brain. So this is the answer to your question, violet is the end of the spectrum, where the Short cone's activity dominates. In fact, you need to add the Long cone's activity to get away from the end of the spectrum, and move towards blue.
It is too correct, that a certain perceived color in the brain can be produced by multiple different combinations of signals from the three types of cones.