Are both sensors supposed to be green?

No, both garage door sensors are not supposed to be green; normally one sensor shows yellow or amber and the other shows green when properly aligned and powered, though colors vary slightly by brand. On most LiftMaster, Chamberlain, and Craftsman openers, the sending sensor, which transmits infrared beam, shows a steady yellow or amber LED when powered, while the receiving sensor, which receives beam, shows steady green LED when it is aligned and receiving beam. Some Genie models use red for sender and green for receiver, or both green on older models, but typical is yellow and green. If both are green, you may have older model where both green indicates alignment, but modern standard is yellow and green. What matters is that LEDs are steady, not blinking or off. If green is blinking or off, receiving sensor not receiving beam due to misalignment, obstruction, dirty lens, or wiring issue, causing door to reverse when closing. If yellow is off, sending sensor has no power due to wiring issue or bad sensor. Both should be steady when aligned: yellow steady on sender, green steady on receiver. If both are off, check power at motor unit and wiring connections. If both blinking, check for loose wiring. Clean lenses and align sensors so they point directly at each other at same height 4 to 6 inches off floor. If LEDs remain off after alignment, sensors may be bad and need replacement costing 20 to 50 dollars pair.