i have x17r1 and that white light shows that the microphone is muted. if you click that button again the mic will switch on.  
Hi, my keyboard on my x15 R1 has that RGB feature. That works for most keys, but the "Mute key" (right side, second from top) is blank white. Is that normal or an error? Best regards
x15 R1, Mute key is white