Gelcoat is mixed on your hull, not picked from a colour fan. The original has had years of sun and has faded, and gelcoat also dries to a different shade than it looks when wet. That is why we work with test pieces that are allowed to cure before anything permanent happens.
Why the yard's code does not work
Yards work with fixed gelcoat colours, and those codes can often still be looked up. Even so, ordering by code is rarely the right route: UV breaks down the top layer of gelcoat and slowly draws the colour out. White goes yellower or chalkier, red fades fastest, blue after that.
Put the original colour next to twenty years of weathered gelcoat and you see the difference immediately, especially on the sunny side of the boat, which has faded harder than the shaded side.
How it is done instead
We start from a base colour and mix in pigment until the colour matches a cleaned, polished patch of your own hull next to the damage. Polish first, because dull gelcoat reads lighter than it is.
Then comes a test piece: a small patch that is left to cure and that we hold against the hull. Gelcoat shifts in shade as it cures, so judging it wet always produces a miss.
Only when the test piece is right does it go onto the repair. On difficult colours two or three test pieces are needed, and that is normal.
What you may realistically expect
On white and light colours the result is almost always undetectable, even close up. On dark blue, red and black a minimal difference sometimes remains that you see from fifty centimetres and not from the jetty.
We say so beforehand, because the disappointment is always in the promise, not in the work. Anyone guaranteeing invisibility on a weathered red hull is promising something physics does not allow.
If a seamless hull is the requirement anyway, respraying a whole panel is the honest route. That costs more, but then the colour runs through to a natural break such as a side deck or an edge.