Hello,
John Lambert and Alan Raven are correct with the colours G45, B15 and white. Alans patterns are also generally correct.
However, as with anything that is 60+ years old, there will be variations and discrepancies that may not be known to all.
The WEM paints are very good and mostly correct, but there are some sources that show slight differences. Again, not surprising since the standards spanned years and countries in the throws of war.
The photo below shows some Fairmile D's at a Jetty in England, late war. For those that wish to discount colour footage, go ahead, but the colours I see are close enough to the samples below the pic that I take them for correct enough for me.
The boats show a light design near the jetty, with a dark one next and another light one. The dark design varies slightly from Ravens book with the additions of a band of B15 at the bow.
The shadows make the G45 show up as a couple of different shades and the decks have some glare, but are definately B15 on the left 2.
The following images are photos I took in Ottawa at the Defence History Directorate. It is a colour chip book from 1945. I photographed it on top of the Snyder and Short paint chips used by WEM to mix their paints. Raven and Snyder combined thier research to come up with these colours. The lighting and camera image isn't great, but it compares reasonably well when examined beside the S&S cards.
The G45 from the 1945 card is much bluer and compares favourably to the G45 in the previous pic. G45 is the side panel on the hull that starts at the top and goes back, getting wider. It is also the colour of the superstructure.
B15 is the colour of the decks, torpedo scallops and the bit on the bow of the second boat.
So I present these for your reference to do with as you wish. Good luck!!