You show above .the visible light frequencies, which are the colors of the rainbow. Visible light is composed out of elementary particles called photons whose energy is given by $E=hν$, which are mathematically described by wavefunctions that are solutions of the quantized Maxwell equations. A quantum superposition of zillions of photons build up the classical electromagnetic wave. Visible frequencies are a small part of the spectrum..
But there is another aspect of color, called color perception, what hits the retina in our eye and the brain assigns a color to it.
If I got it right, then light is a particle
No, light is a superposition of quantum mechanical zero mass photons
which has magnetic and electric energy and this energy is oscillating all the time.
Only in the superposed composed of zillions of photons classical wave. The particle/photon has a fixed energy and is neutral, the electric and magnetic fields are built up by the superposition of zillions of photons. The photon itself, just has energy, and spin and momentum. The electric and magnetic fields are in the complex wavefunction whose complex conjugate squared gives the probability of finding a photon at x,y,z. See this experiment.
So seeing a color does not define uniquely the frequency.
that is correct.
To answer whether single photons/ quanat exist, here is the double slit experiment single photon at a time
Single-photon camera recording of photons from a double slit illuminated by very weak laser light. Left to right: single frame, superposition of 200, 1’000, and 500’000 frames.
It is a quantum of the light, and the frequency can be extracted from using slit width, distance and the accumulated interference pattern of the classical manifestation. After all the wave nature is in the probability distribution displayed nicely here on the right.
Is it a wave packet hitting singly and seemingly randomly on the left? each point could be modeled with a narrow wavepacket consistent with the frequency.
For absorption and emission sectra , the lines have a width, and the wavepacket if within the frequency width will act as one quantum, imo.