Thankfully people don't book based on a plane's colour scheme. They look at things like route structure, frequency, punctuality and price and when people consider these things U2 can be attractive. With the same/similar legroom as BA and better punctuality than BA and with BA now charging for bags, it's easy to see why people are happy to skip the 'free' snack (20g packet of 'hand cooked crisps' or a small sandwich at best).
Watch any UK/FR domestic or any CDG/AMS/CPH/NCE/BCN/MAD flight on U2 and you'll notice there's no shortage of suits who happily travel U2.