The Sam in the Gray Flannel Suit - S6-E20
Corrected entry: Sam and Rebecca are in his office talking and he is wearing a tan suit with brown shoes. He leaves in a hurry to go into a sales meeting in Evan's office, and he comes in wearing a dark suit with dark shoes.
Correction: I have seen this episode and recently re-watched it twice, and Sam is wearing the same brown suit, tie and shoes in each scene (in the office with Rebecca and when he goes to the sales meeting).
Kitty1019