The grey-green suit and open white shirt create a quieter alternative to a short closed bow tie. A small pale square appears at the breast pocket. One hand rests in a pocket and a leg bends at the doorway; beige slip-on shoes have pale soles. Dark sunglasses are worn. Complete footwear is visible, although the stance is not neutral. Colour and open collar offer styling information rather than confirmed provenance or universal occasion suitability. Consider how much space the open shirt takes between the lapels and how the small square sits beside that opening.
If an open collar suits your actual setting, compare it with a bow tie on the same jacket. Assess shirt opening and space between the lapels first. Insert the intended square next and decide whether the upper outfit already has enough emphasis. Bow size cannot be estimated only from an open collar: close the real shirt for that second fitting. Add a straight standing view in your own shoes for the hem. These are complete separate choices, not an automatic switch for every invitation, and the closed collar needs its own proportions assessed.