The color you see when you look at a "sensor" is usually determined by the combined colors of the colored filter arrays that are placed directly in front of the actual silicone chip as well as the combination of other filters (Low-pass, IR, UV) placed in the "stack" in front of the sensor.
Although we call them "red", "green", and "blue", the colors of most Bayer masks are:
- 50% "green" pixels that are centered on around 530-540 nanometers and significantly sensitive to light ranging from about 460nm to past 800nm and the edge of the infrared range. The "color" of 540nm light is perceived by most humans as a slightly bluish green color.
- 25% "blue" pixels that are centered on around 460nm and significantly sensitive to light ranging from the non-visible ultraviolet range to about 560 nm. The "color" of 460nm light is perceived by most humans as a bluish-violet color.
- 25% "red" pixels that are centered on around 590-600nm and significantly sensitive to light ranging from about 560nm to well into the infrared range. The "color" of 600nm light is perceived by most humans as a yellowish-orange color. (What we call "red" is on the other side of orange at about 640nm).
The "color" components of the Bayer mask can be seen by looking at spectral response curves for various sensors:
The "colors" each type of cone in the human retina are most sensitive to are similar:
Here is a representation for the "colors" humans perceive for various wavelengths of light:
Please compare the peaks of the sensitivities above with the "colors" of those wavelengths along the visible spectrum.
There are no coatings on most tri-color imaging sensors that is centered on what we call "red", all of the drawings on the internet of CMOS sensors with Bayer filter arrays depicted notwithstanding.
Most CMOS sensors placed in cameras used for taking the types of images we consider "photography" here have a "stack" of filters that include both infrared (IR) and ultraviolet (UV) cut filters in front of the Bayer color filter array. Most also include a low pass "anti-aliasing" filter. Even sensor designs that are said to have "no low pass filter" tend to have either a cover glass with the same refractive index or the two components of a low pass filter oriented to each other so that the second one cancels the first one.
What one sees when one looks into the front of a camera and sees an exposed CMOS sensor is the combined effect of light reflecting off all of theses filters, and is dominated by the slightly bluish-green tint of the "green" filtered portions of the Bayer mask combined with half as many blue-violet and orange-yellow filtered portions that we call "blue" and "red". When viewed sitting inside an actual camera, most of the light striking the sensor and the stack in front of it will be from a fairly narrow range of angles and usually be fairly uniform in color. (The purple tint on the edge of the Sony sensor is probably due to reflections of light at just the right angles off the UV and/or IR cut filters.)
When there is light from a wide range of angles falling on such a sensor without the filter "stack" in front of it, there will also be a prismatic effect evident that will show a fuller range of colors, due to the shapes of the surface of the microlenses on top and the colors of the Bayer mask sandwiched in between the microlenses and the sensor.