WIRELESS SD SHIELD

if anyone has this shield i have set it up according to the logic implied on the shield's labelling & common sense. The TX & RX LED indicators are both green so is the PWR led is on and the RSSX led is yellow. Is this an indicator of signal strength? i have not pinned a Wifi module yet but was wondering if the shield itself has some kind of RF sensor or its just yellow to differentiate it from the others.