A B757-200 DEADHEADING COMPANY CAPT POINTED OUT THAT THE ACFT WINGS WERE CONTAMINATED WITH FROST. THIS OCCURRED ON TAXI TO THE RWY.

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FROSTY WINGS. A SUNNY; CLR; YET COLD MORNING FOR DEP FROM ZZZ. A SPECIAL QUALIFICATION CITY IN MOUNTAINOUS TERRAIN. NO SPECIAL REASON FOR CONCERN ABOUT THE CONDITION OF THE ACFT OR MY FO; WITH WHOM I HAVE ENJOYED A GOOD MONTH OF TROUBLE-FREE FLYING. NORMAL SEQUENCE OF EVENTS IN PREPARATION FOR START; TAXI; ETC; UNTIL A CABIN CALL CAME TO THE COCKPIT. A FELLOW DEADHEADING COMPANY PLT; RIDING IN MAIN CABIN RPTED THROUGH ONE OF OUR FLT ATTENDANTS THAT THERE WAS FROST PREVALENT ON THE TOP SURFACES OF BOTH WINGS. I DECIDED IMMEDIATELY TO RETURN TO THE RAMP FOR DEICING. ATC; STATION PERSONNEL; AND PAX WERE ADVISED OF THE CIRCUMSTANCES AND OUR INTENTIONS AS WE RETURNED FOR DEICING. A ZZZ RAMP AGENT AND A DEICER GUIDED US TO A RAMP-SIDE DEICING PAD FOR DEICING WITH TYPE I FLUID. ONCE COMPLETE; WE RESTARTED ENGS; AND RESUMED TAXI OUT AND A SUBSEQUENT NORMAL; UNEVENTFUL TKOF INTO A BEAUTIFUL ROCKY MOUNTAIN MORNING. THE FO IS A DILIGENT PROFESSIONAL. I'M CONFIDENT IN HIS ABILITY AND PERFORMANCE. THIS MORNING; HOWEVER; THE COFFEE JUST WASN'T DOING THE TRICK; AND HE ADMITTEDLY FAILED TO ADEQUATELY CONFIRM THAT THE WINGS WERE CLEAN. TEMP WAS SEVERAL DEGS BELOW FREEZING; ALTHOUGH THE AIR WAS RELATIVELY DRY. NO EVIDENCE OF FROST WAS PRESENT ON THE UNDERSIDES OF THE WINGS; SO HE CONCLUDED THE TOPS MUST ALSO BE FROST-FREE; WITHOUT ACTUALLY HAVING EXAMINED THE UPPER WING SURFACES. IF A GLANCE BACK FROM THE REAR OF THE ACFT HAD BEEN MADE DURING THE WALKAROUND; THE FROST WOULD HAVE BEEN SPOTTED; AND DEICING WOULD HAVE BEEN CALLED FOR PRIOR TO TAXI OUT. BESIDES THE OPPORTUNITY FOR FROST DETECTION DURING THE NORMAL EXTERIOR WALKAROUND SEQUENCE; A GOOD PRACTICE TO ALLEVIATE THE RISK OF SUCH AN EMBARRASSING AND POSSIBLY CRITICAL OVERSIGHT AS THIS MAY BE TO MAKE A HABIT OF CHKING WING SURFACES FROM WITHIN THE CABIN IN THE CASE OF PREFLT IN SUCH FREEZING CONDITIONS. I; TOO; SHOULD SIMPLY MAKE IT A HABIT TO MAINTAIN A DEGREE OF SKEPTICISM ABOUT THE POSSIBILITY OF ICE OR FROST ON THE ACFT WHENEVER AN ACFT HAS BEEN OVERNIGHT AT SUB-FREEZING TEMPS. I'LL ASK RATHER THAN ASSUME. MY QUERY DURING COCKPIT PREPARATIONS MAY HAVE PROMPTED ONE MORE CHK WHICH WOULD HAVE REVEALED THE CONTAMINATED WINGS. MANY THANKS TO NON-REVENUING CAPT FOR HIS INTERVENTION. HIS INPUT SPARED US FROM MAKING A TKOF WITH CONTAMINATED WINGS.