Should both my garage door sensor lights be green?

Whether both sensor lights should be green depends entirely on the brand. On Genie Safe-T-Beam systems, yes, both sensors are designed to glow solid green when the door is working properly. On LiftMaster, Chamberlain, and Craftsman, no, only the receiver sensor lights green and the sender sensor lights amber or orange. Both being green on a LiftMaster is actually unusual and sometimes indicates a non-original aftermarket sensor. Check the brand of your opener first by looking at the motor unit on the ceiling. Then look up the correct color pattern for that brand. As long as both sensors are lit steady and the colors match the manufacturer's spec, your safety system is aligned and working.