All stars have approximately a blackbody curve as their spectrum. The sun’s spectrum happens to peak around green, and our eyes are calibrated to interpret that as neutral (white). Other stars can only have that peak shifted towards blue/violet (when hotter) or towards yellow/orange/red (when cooler), which to our eyes correspondingly looks more blue/violet or more yellow/orange/red. If our sun peaked at red or blue, we would probably be able to see green stars.