I am using Archer 60 Router as I have confusion in LED configuration as in stock firmware when Internet goes down my Wan Led change colour to amber colour. But it does not turn in Openwrt Firmware.
Without any first-hand experience with the Archer 60: The stock firmware probably tests the WAN connection in regular intervals, then turns on one of two LEDs (green or amber) depending on the result.
OpenWrt does not do that out of the box. If you're using PPPoE/PPPoA for WAN it can actually show the state of the connection on the WAN LED. But if you're using DHCP (or fixed IP) on the WAN port, the WAN LED will light as soon and as long as a cable is inserted, you would need to write a custom script to replicate the LED behaviour.
If my memory serves my right, you can configure the LEDs on the ethernet interface, or the pppoe interface.