The orange suits (affectionately called pumpkin suits) are not spacesuits. They are worn only while inside a vehicle that is ascending or descending through the atmosphere. Their primary purpose is to protect the crew member from the adverse effects of a depressurization inside the vehicle. They are orange because orange creates a high contrast against the background for rescue crews looking for the crew members in the water or on land.
The current white suits are spacesuits. They are designed for use outside the vehicle, in the vacuum of space. They are designed to provide a pressurized environment, thermal control, and protection against tears and punctures. The suits are white because of emittance. A spacesuit is a thermal system. It is therefore designed to balance the flow of heat into and out of the system. The heat from the Sun is part of the equation, but it is not the full equation. The human being and electrical equipment that is inside the suit is also producing heat and that (excess) heat needs to be rejected.
Credit : Quora
Picture Credit : Google