B757 CREW; OPERATING IN SNOW; HAD A PAX POINT OUT THAT THE ACFT NEEDED DEICING IN PIT.

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CONCERNED ABOUT THE WX (10 SM; SNOW; 070 OVCST; 1 MI VISIBILITY) BOTH THE CAPT AND FO CHKED THE WINGS FOR CONTAMINATION FROM THE CABIN AT THE GATE PRIOR TO BOARDING. IN ADDITION; THE FO DID THE REQUIRED PREDEP ACFT CHK DURING HIS WALKAROUND. WE BOTH CONCLUDED THE ACFT WAS CLEAN. AFTER DISCUSSION; THE CURRENT WX CONDITIONS AND CONSULTING A COMPANY PROVIDED DE-ICING/ANTI-ICING FLOW CHART WE DETERMINED THAT DEICING WOULD NOT BE NECESSARY. WHEN WE WERE #1 FOR TKOF; A FLT ATTENDANT CALLED THE COCKPIT TO RPT THAT A COMPANY EMPLOYEE TRAVELING AS A PAX AND FAMILIAR WITH DEICING PROCS AND REQUIREMENTS HAD DETERMINED THAT THE WINGS WERE CONTAMINATED AND THAT THE ACFT REQUIRED DEICING. WE DECIDED TO GO TO THE DEICE PAD AND REQUEST AN EXTERNAL INSPECTION BY DEICING PERSONNEL. DEICING PERSONNEL DETERMINED THAT A TYPE I WASH WAS NEEDED. IT IS WIDELY RECOGNIZED THAT SOME KINDS OF CONTAMINATION ARE NEARLY IMPOSSIBLE TO DETECT FROM THE GRAZED WINDOW IN THE CABIN. THIS EVENT UNDERSCORES THE POINT. NEEDLESS TO SAY; GOOD PROC MANDATES AN EXTERNAL INSPECTION WHENEVER WX CONDITIONS ARE QUESTIONABLE.