Should one garage door sensor be red and green?

Whether one garage door sensor should be red and green depends entirely on the brand and model of your opener, because different manufacturers use different color codes. On many Genie and Overhead Door systems, it is completely normal to have one sensor with a solid red LED and the other with a solid green LED when everything is working correctly. In that system, red typically indicates the sending sensor that is emitting the infrared beam and has power, while green indicates the receiving sensor that is aligned and receiving the beam. However, on LiftMaster, Chamberlain, Craftsman, and Stanley openers, you will almost never see red and green as the normal state. Those brands use a solid yellow or amber light on the sender and a solid green light on the receiver. If you have a LiftMaster system and you are seeing red, it usually means a fault, overheating, or you are looking at a different type of sensor such as the motion sensor or wall button. Always check the small label printed on the sensor housing or your owner's manual for the exact color legend for your specific model year.