It may have to do with the wavelengths and frequencies of the light waves. Blue has a shorter wavelength than green and so the blue light scatters faster than green and reds.

Though I am not going to explain it well, this is the same reason that the sky is blue and sunsets are reddish.

Here is a link that will do a much better job than I can. https://scijinks.gov/blue-sky/

It could just be the binoculars - maybe the lens and/or coating is not the same on both sides.
Does the same thing happen with a different pair?