The green dots in the Devices tab indicate the device is registered at the DNS-SRV server while the yellow dots indicate the device is registered at the A-Record (Legacy) server. Both green and yellow dots show that the device is registered and should work properly. 


The main difference is the mechanism of ensuring registration in case of a server failure, with DNS-SRV the interruption is minimized while using the A-Record registration renewal could take up to 5 minutes (300 seconds), so DNS-SRV is the preferred way.