If it’s red, it means that G-SYNC is enabled. Note that G-SYNC only works with NVIDIA cards, and unless your card is a GTX 960 or above, I wouldn’t really recommend buying this monitor. Another way to test if G-SYNC is working is to open NVIDIA Control Panel, click on Change resolution, then select Display at the top, and tick G-SYNC Indicator.
https://www.amazon.com/PG279Q-DisplayPort-Adjustable-Ergonomic-EyeCare/dp/B017EVR2VM

