Question: "What determines the colour of light ? Is it the wavelength or the frequency of the light?"

Answered.....

"When a light photon hits the surface of an object, it transfers its energy to the atoms of the object, causing electrons in the outermost orbits of the atoms to absorb the photon, becoming some free electrons. The resulting photon is emitted according to the corresponding wavelength and then enters our eyes, so we see the color of the object according to the corresponding wavelength of the emitted photon."

The retina is covered with millions of light sensitive cells called rods and cones. When these cells detect light, they send signals to the brain. Cone cells help detect colors. Most people have three kinds of cone cells, these three types of cones allow us to see a certain range of the visible light spectrum on the electromagnetic spectrum, translated into colours, these colours are blue, green, and red and are called primary colours.

A monitor or TV screen generates three colors of light (red, green, and blue) and the different colors we see are due to different combinations and intensities of these three primary colors. In its most basic form, a color broadcast can be created by broadcasting three monochrome images, one each in the three colors of red, green, and blue (RGB). When displayed together or in rapid succession, these images will blend together to produce a full-color image as seen by the viewer. 

However, most of the time we see sunlight and the colors of surrounding objects, naturally, when light photons fall on the objects.

Sunlight, or visible light, are actually white in color and form a mixture of the seven colors we see in a rainbow, i.e., made of all the rainbow colors: red, orange, yellow, green, blue, indigo, and violet.

The colour of visible light depends on its wavelength. These wavelengths range from 700 nm at the red end of the spectrum to 400 nm at the violet end. Visible light waves are the only electromagnetic waves we can see. We see these waves as the colours of the rainbow. Therefore, the human eye can detect wavelengths from 380 to 700 nanometers. 

Here are from shortest to longest wavelengths of light:

• Violet - shortest wavelength, around 400-420 nanometers with highest frequency. 
• Indigo - 420 - 440 nm.
• Blue - 440 - 490 nm.
• Green - 490 - 570 nm.
• Yellow - 570 - 585 nm.
• Orange - 585 - 620 nm.
• Red - longest wavelength, at around 620 - 780 nanometers with lowest frequency.

When light falls on the object some of it is reflected, some are transmitted and some are absorbed. The reflected rays give colours to the objects and the reason why we see things. Objects appear different colours because they absorb some colours (wavelengths of light) and reflect or transmit other colours. The colours we see are the wavelengths that are reflected or transmitted.

When a light photon hits the surface of an object, it transfers its energy to the atoms of the object, causing electrons in the outermost orbits of the atoms to absorb the photon, becoming some free electrons. The resulting photon is emitted according to the corresponding wavelength and then enters our eyes, so we see the color of the object according to the corresponding wavelength of the emitted photon.

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