Since he'll be looking at it just after it's painted to decide whether he likes the result or not, looking at an old faded boat isn't going to be helpful... π
Either way photos and anything viewed on-screen really can't be relied on, it depends too much on the camera/screen -- on my monitor right now the photos I posted look pretty close to real life (because I have the RAL swatches here to compare with), but that may not be true on a different monitor, or even if different lighting. Lighting conditions make a big difference, as I found out with reds -- the one I chose (Signal Red) was much more orange in real life and bright sunlight than I was expecting, given that I looked at the swatches in dull winter light... π
If he can't find a boat in the right colour @STIG is welcome to borrow my RAL swatch book if he's anywhere nearby, otherwise I'd suggest lashing out Β£50 or so on one of his own. It sounds expensive but it's much cheaper than having to get a colour changed afterwards... π