Why do they paint interior green the interiors of aircrafts and not just any other color?

Short answer is they don't paint them Interior Green.

Long answer. Interior Green is the name given to the color seen in most non-modern US cockpits. The true coating is Zinc Chromate. You may have heard of Zinc Chromate Green and Zinc Chromate Yellow. In reality they are actually the same thing. Zinc Chromate is a corrision resistant material that is added to a carrier and sprayed on the interiors of aircraft cockpits and interior portions. Zinc Chromate in itself is a yellow-green color and the carrier was usually untinted. Military standard was to give only one coat of the Zinc Chromate primer. As we all know one coat of paint will often be affected by the color it's painted over. Therefore, when painted over white surfaces Zinc Chromate appears to be a yellowish (Zinc Chromate Yellow) color and when applied to bare metal will be a an apply green color (Zinc Chromate Green or Interior Green). Sometimes Zinc Chromate was mixed with Lamp Black paste to give it a bit more UV resistance, this would bring out the green a little more as well.

HTH