B757 FLT CREW; WHILE TAXIING TO TKOF; IS NOTIFIED BY A DEADHEADING PLT RIDING IN THE CABIN THAT HE OBSERVED FROST ON THE WING'S UPPER SURFACE. FLT CREW RETURNS TO THE GATE AND THE ACFT IS DEICED.

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WE WERE LEAVING ON THE FIRST FLT OF THE DAY FOR OURSELVES AND OPS. WX WAS CLR WITH TEMP 0 DEGS C. I WENT TO OPS FOR PAPERWORK WHILE FO WENT DIRECTLY TO ACFT TO ACCOMPLISH PREFLT/WALKAROUND. IF WE NEEDED DEICING IT WOULD BE DONE JUST OFF THE GATE. ARRIVING AT ACFT I ACCOMPLISHED PREFLT DUTIES. FO NEVER MENTIONED ANY ICE ON ACFT OR NEED FOR DEICING. ON TAXI OUT; FLT ATTENDANT CALLED TO SAY A DEADHEADING PLT RPTED FROST ON WINGS. HE GOT ON THE INTERPHONE AND IDENTED HIMSELF AS A PLT DEADHEADING AND OBSERVED FROST ON THE WINGS. I ASKED THE FO IF HE HAD NOTICED ANY ICE ON THE ACFT AND HE SAID 'NO.' WE TAXIED BACK TO GATE FOR DEICING FOLLOWING DEICING PROCS. TKOF; ENRTE AND LNDG WERE NORMAL. POOR LIGHTING DURING PREDAWN DARKNESS RESTR ACFT VISIBILITY. NEVERTHELESS; I SHOULD HAVE BEEN MORE PROACTIVE BY ASKING THE FO ABOUT ACFT ICE. SUPPLEMENTAL INFO FROM ACN 687210: I WAS RIDING AS A PAX. PRIOR TO PUSHBACK I NOTICED A SIGNIFICANT AMOUNT OF FROST ON THE OUTBOARD THIRD OF THE R WING. THIS COVERED THE WING; SPOILER PANELS AND AILERON. I ASSUMED THE CREW WAS AWARE OF THE SITUATION AND THAT THE ACFT WOULD BE DEICED PRIOR TO FLT. IT BECAME APPARENT THAT THE CREW DID NOT KNOW ABOUT THE FROST WHEN THEY STARTED ENGS AND JOINED THE TXWY FOR DEP ON RWY 34. I WENT TO THE AFT GALLEY; CALLED THE COCKPIT; IDENTED MYSELF AS A DEADHEADING PLT AND EXPLAINED THE SITUATION. THE ACFT RETURNED TO THE GATE AND WAS DEICED. THE FLT THEN PROCEEDED WITHOUT FURTHER INCIDENT.