Continuity mistake: The morning after Vivian's first night at the hotel, room service brings breakfast. When she's eating a croissant it cuts to a shot of Edward, and when it cuts back to Vivian she's eating a pancake which goes from being half done, to being a whole pancake again. (00:30:55)
Continuity mistake: When Stuckey hits Vivian she rips his watch off. You can see it fly off to the left. When she bites him it's back on his wrist. Then when Edward pulls him off Vivian it's gone again. (01:00:20)
Continuity mistake: At the hotel, when Vivian and Edward sit in Edward's room, for the first time, she shows him a selection of different coloured condoms. The order of those condoms changes, between the shots facing her and the shots facing her back.
Continuity mistake: When Vivian is standing at the elevator at the hotel after the polo match trying to leave because she is mad at Edward, the arrangement of clothes and her arms changes between shots. (01:17:45)
Continuity mistake: When Vivian and Edward are arguing, she asks for her money, so he reaches for his wallet and takes the money out. When he drops the money on the bed, part of the money is lying on the corner of his suit jacket. After Vivian walks out, when he turns to see if she took the money, it is not lying on his jacket, but at the edge of the bed.
Continuity mistake: After Vivian is hired and she jumps on the bed shouting "$3,000!" the position of the pillows changes between shots. (00:37:25)
Continuity mistake: In the screen where Vivian has been on the shopping spree, she returns to the hotel wearing the cream colored dress and a black hat. When she walks into the hotel, her black purse is under one arm. Then they show a behind shot of her walking away and the purse is under the other arm.
Chosen answer: Posters are usually designed long after the film has been made, and by the marketing department. Decisions about the outfit may have been based solely on what was considered best by the marketing department (for instance, to match the color of the lettering in the title.) Also, Julia Roberts' head has been super-imposed onto a model's body in the poster image (just as Richard Gere's hair has been darkened). These are all creative marketing decisions.