My views , shoukd nobody feels agitated, Gurbani says " Rang sabhey narainey jetey man bhavann ." ( ang 134- 3, Baramaha Manjh M5) Nature and colors are all made by Waheguru, parmeshar himself , how come One is bad and other good.
Because green was the color of moghul army flag , the use in khalsa dal was taboo to avoid misundestanding during battles, and for the same reason red was banned as pahadi rajas , who were perpetually at war with guru sahib ji . It was simple logicand practice without religious adsignment for colors. Did not guru sahib had many muslims and hindus on his side?