Some animals see colour as we do, some see it in shades of grey and some see it in monochromatic ( Black and white )
Deer for example see it in shades of greys so the bright colours are not as obvious to them as to us humans. The bright orange is obvious to us but to the stag / doe , its just a series of shades of grey -
Has to do with the receptors in the back of the eyeball - humans and deer have different receptors - Ain't nature grand

I have always hunted with a bright red or orange hat on my head - that way i can be seen but not seen. And ive shoot more than a few deer who were looking directly at me at the time, they can see me but they can define me.
Its also why in the US its mandatory in most states to wear orange - stops hunters being shot by other over enthusiastic hunters ( sometimes)
- they do lose one now and then as some idjit doesnt bother to check who/what he is actually shooting at. Has happened here in Victoria Aust. - Moral of the story tho, always identify what your shooting at or dont shoot at all !!! - Buck fever can be fatal for other than the buck.