Why is the Pope's helmet of SS Gemini red, and all other popes seem to be gold?

Because in the animated version, you usually see the Pope is Alex, not Shi Ang. Pope's helmet is yellow, that is, Shi Ang's helmet is yellow. Alex (Shi Ang's younger brother) began to assist Pope Shi Ang before his death, that is, Shi Ang wore a yellow helmet and Alex wore a red helmet.

After SaJia assassinated Alex and Shi Ang successively, he put away Shi Ang's papal robe, his yellow helmet and Alex's red helmet, and played them alternately at the appropriate time. Wear Shi Ang's costume when you need to play Pope Shi Ang, and Kia Lux's costume when you need to play Alex.

In the animated version, the person who presented the bronze sacred clothes of Pegasus to Saint saint seiya was Pope Shi Ang, posing as Sakya, wearing a yellow helmet at that time; In addition to this traditional courtesy and formal ceremony, Issachar pretended that Shi Ang was unwell and refused to attend. Instead, his brother Alex acted as the pope (Alex is the silver saint on the altar, and the saint of this constellation has always acted as the acting pope). At this time, Issachar pretended to be Alex in power, so most of the popes you saw in the sanctuary were Issachar pretending to be the image of Pope Alex, that is, the pope with a red helmet.

After Saint saint seiya's flying horse sacred garment appeared, and the Galaxy Challenge held by the goddess Athena Yarn Weaving in Japan began, Sakya noticed the position of the real goddess and the golden sacred garment, and thought that the real enemy (Athena) appeared. In order to better deal with the goddess, Zacharias decided to officially announce that the former Pope Shi Ang had passed away, and he replaced the Pope as Alex, thus ruling the sanctuary without scruple in all aspects, so as to unanimously oppose Athena. So the image of the Pope after the Galaxy Challenge is the image of Alex's red helmet.