I have done a couple of minor contracts with P&O through one of my businesses and although they did have some frameworks and templates for font/inks/colours etc etc for the branding , they were fairly relaxed once things were proposed to them, if they are on the shirt fronts, I wouldn't expect necessarily the logo is on a white block. For one, if the shirt has white on it already , then a bespoke shape around the logo image and scripting would make the advert easier to see , which is the whole point of shirt advertising in the first place.