Cleaning boat upholstery

So I searched and could not find what I was looking for so throwing this out there....I have white, grey, and black upholstery. I clean it all the time but everytime we use the boat it gets really dirty and the white turns into grey. I wash it and can not get the brilliant white back unless I scrub and scrub and scrub...anything I can put on so I don't have to really work to get the white back or any product that will bring the white back? Help!!!!!