The general consensus is that the stripes on the side were, as of 1805, yellow ochre - whatever that means. There were no official paint colors in the nineteenth-century Royal Navy, so there's some room for personal taste. Most serious Victory modelers, I think, use a dull, somewhat brownish or even slightly orangish shade. A couple of hobby paint companies, Model Shipways and Testor's Acryl, make colors labeled "yellow ochre" that are intended to be used for this purpose. Those colors are as good guesses as any, but there's no definitive "right" one.
Several threads in this Forum deal specifically with the Victory. You'll find that surfing your way through them is a lot of fun - and there's a great deal of information to be found there. Among other things, you'll find links to the ship's website, which has a page dedicated to modelers.
Good luck. It's a great hobby.
Youth, talent, hard work, and enthusiasm are no match for old age and treachery.