camera – Why does my eye lose white balance and feel exhausted when I use my viewfinder?

My D80 has a greenish tint effect (shutter count at approx 46000) in it’s viewfinder which goes away if i use it long enough constantly looking through the viewfinder.

The weird thing is my other eye starts to see things in green tint when i use it for viewfinder instead.

I don’t keep my both eyes during shooting (neither when it comes to shooting certain devices) for easier manual focus but this was a interesting effect.

The other thing i find weird is that my left eye feels exhausted if i keep both of my eyes open.

So, is this normal? What are these called.