Why does my eye see a green tint and feel tired after using an optical viewfinder?

We see using a combination of eye and brain. Our visual response is so complex, many aspects are still not fully understood.

Light receptors imbedded in the retina are divided into two types. Highly sensitive rod-shaped cells in the periphery see only in black & white. The central part of the retina, called the macula, contains pigmented cone-shaped cells, Three types of cone cells, one for each of the light primary colors, red, green, and blue. Recently discovered, some few individuals have a fourth type giving them extraordinary color vision.

The sensitivity of these cells (call it an involuntary ISO adjustment) is remarkable. Under dim conditions, Rhodopsin (visible violet) pigment is secreted and bathes the retina causing the sensitivity (dark adaption). It happens in about 10 minutes, however full dark adaption takes about two hours.

This phenomenon is eye independent. Sailors, going on night watch wear an eye patch over one eye. This covered eye will dark adapt, so when the night watch begins, that eye is fully adapted. Thus, pirates are often depicted wearing an eye patch.

Same for color vision adaption (call it auto white balance). Don colored sunglasses and both eyes adjust their color sensitivity. Color adaption takes place every minute of every day. You are not aware, because it usually happens to both eyes simultaneously.

Try this experiment: Mount a strong color filter over just one eye. This can be photo filter or colored cellophane candy wrapper. Hold it in place for a few minutes. Now remove and look about, winking one eye and then the other. You will immediately see the amazing ability of eyes to auto color balance. If you mount a red filter, that eye will have reduced red sensitivity, and when you remove the filter, for several minutes, your vison from that eye will be tinted cyan.

In other words, the change is towards the complementary color (opposite or negative). Don a red filter; the after effect is cyan. Don a cyan filter; the after effect is red. Don a blue filter; the after effect is yellow. Don a yellow filter; the after effect is blue. Don a green filter; the after effect is magenta. Don a magenta filter; the after effect is green.

This auto adaption makes it hard to see abnormal hues in everyday life. On images are more accurate than you might think but we view them under a different color of light and now we see the color balance as wrong.

Nobody said this stuff is easy!